Power control and power headroom reporting for dual connectivity

ABSTRACT

The present disclosure relates to a method for efficiently performing power control in situations where the UE is connected to both a MeNB and SeNB. The MeNB determines a power distribution ratio for the power to be used by the UE for uplink transmission to the MeNB and SeNB, determines the parameters P EMAX,MeNB  and P EMAX,SeNB  and sends these parameters to the SeNB/UE for use in power control. Moreover, update of the power distribution ratio is performed by the MeNB with assistance by the UE, which provides the MeNB with information on the pathloss on the secondary radio link to the SeNB, preferably by transmitting a virtual power headroom report, regarding the secondary radio link to the SeNB, to the MeNB, from which the MeNB derives the information on the pathloss for the secondary radio link.

TECHNICAL FIELD

The present disclosure relates to methods for an improved power headroomreporting and power distribution control. The present disclosure is alsoproviding a mobile station and base stations for participating and forperforming the methods described herein.

BACKGROUND

Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving a radioaccess technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies, 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support for the next decade.The ability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTEsystem represents efficient packet-based radio access and radio accessnetworks that provide full IP-based functionalities with low latency andlow cost. In LTE, scalable multiple transmission bandwidths arespecified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order toachieve flexible system deployment using a given spectrum. In thedownlink, Orthogonal Frequency Division Multiplexing (OFDM) based radioaccess was adopted because of its inherent immunity to multipathinterference (MPI) due to a low symbol rate, the use of a cyclic prefix(CP) and its affinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA) based radioaccess was adopted in the uplink, since provisioning of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmit power of the user equipment (UE).Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniquesand a highly efficient control signaling structure is achieved in LTERel. 8/9.

LTE Architecture

The overall architecture is shown in FIG. 1 and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2. TheE-UTRAN consists of an eNodeB, providing the E-UTRA user plane(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towardsthe user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY),Medium Access Control (MAC), Radio Link Control (RLC) and Packet DataControl Protocol (PDCP) layers that include the functionality ofuser-plane header-compression and encryption. It also offers RadioResource Control (RRC) functionality corresponding to the control plane.It performs many functions including radio resource management,admission control, scheduling, enforcement of negotiated uplink Qualityof Service (QoS), cell information broadcast, ciphering/deciphering ofuser and control plane data, and compression/decompression ofdownlink/uplink user plane packet headers. The eNodeBs areinterconnected with each other by means of the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (SGW) by meansof the S1-U. The S1 interface supports a many-to-many relation betweenMMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user datapackets, while also acting as the mobility anchor for the user planeduring inter-eNodeB handovers and as the anchor for mobility between LTEand other 3GPP technologies (terminating S4 interface and relaying thetraffic between 2G/3G systems and PDN GW). For idle state userequipments, the SGW terminates the downlink data path and triggerspaging when downlink data arrives for the user equipment. It manages andstores user equipment contexts, e.g. parameters of the IP bearerservice, network internal routing information. It also performsreplication of the user traffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theSGW for a user equipment at the initial attach and at time of intra-LTEhandover involving Core Network (CN) node relocation. It is responsiblefor authenticating the user (by interacting with the HSS). TheNon-Access Stratum (NAS) signaling terminates at the MME and it is alsoresponsible for generation and allocation of temporary identities touser equipments. It checks the authorization of the user equipment tocamp on the service provider's Public Land Mobile Network (PLMN) andenforces user equipment roaming restrictions. The MME is the terminationpoint in the network for ciphering/integrity protection for NASsignaling and handles the security key management. Lawful interceptionof signaling is also supported by the MME. The MME also provides thecontrol plane function for mobility between LTE and 2G/3G accessnetworks with the S3 interface terminating at the MME from the SGSN. TheMME also terminates the S6a interface towards the home HSS for roaminguser equipments.

Component Carrier Structure in LTE

The downlink component carrier (CC) of a 3GPP LTE system is subdividedin the time-frequency domain in so-called subframes. In 3GPP LTE eachsubframe is divided into two downlink slots as shown in FIG. 3, whereinthe first downlink slot comprises the control channel region (PDCCHregion) within the first OFDM symbols. Each subframe consists of a givenumber of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPPLTE (Release 8)), wherein each OFDM symbol spans over the entirebandwidth of the component carrier. The OFDM symbols thus each consistsof a number of modulation symbols transmitted on respective N^(DL)_(RB)*N^(RB) _(sc) subcarriers as also shown in FIG. 4.

Assuming a multi-carrier communication system, e.g. employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block (PRB) is defined as N^(DL) _(symb) consecutiveOFDM symbols in the time domain (e.g. 7 OFDM symbols) and N^(RB) _(sc)consecutive subcarriers in the frequency domain as exemplified in FIG. 4(e.g. 12 subcarriers for a component carrier). In 3GPP LTE (Release 8),a physical resource block thus consists of N^(DL) _(symb)*N^(RB) _(sc)resource elements, corresponding to one slot in the time domain and 180kHz in the frequency domain (for further details on the downlinkresource grid, see for example 3GPP TS 36.211, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)” (NPL 1), section 6.2, available at http://www.3gpp.org andincorporated herein by reference).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forsake of terminology, in the following the time-frequency resourcesequivalent to the same N^(RB) _(sc) consecutive subcarriers spanning afull subframe is called a “resource block pair”, or equivalent “RB pair”or “PRB pair”.

The term “component carrier” refers to a combination of several resourceblocks in the frequency domain. In future releases of LTE, the term“component carrier” is no longer used; instead, the terminology ischanged to “cell”, which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources. Similar assumptions for the component carrierstructure apply to later releases too.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07). Although the overall frequencyspectrum for IMT-Advanced was decided, the actual available frequencybandwidth is different according to each region or country. Followingthe decision on the available frequency spectrum outline, however,standardization of a radio interface started in the 3rd GenerationPartnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the StudyItem description on “Further Advancements for E-UTRA (LTE-Advanced)” wasapproved. The study item covers technology components to be consideredfor the evolution of E-UTRA, e.g. to fulfill the requirements onIMT-Advanced.

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers (cells) areaggregated in order to support wider transmission bandwidths up to 100MHz. Several cells in the LTE system are aggregated into one widerchannel in the LTE-Advanced system which is wide enough for 100 MHz eventhough these cells in LTE are in different frequency bands.

All component carriers can be configured to be LTE Rel. 8/9 compatible,at least when the aggregated numbers of component carriers in the uplinkand the downlink are the same. Not all component carriers aggregated bya user equipment may necessarily be Rel. 8/9 compatible. Existingmechanism (e.g. barring) may be used to avoid Rel-8/9 user equipments tocamp on a component carrier.

A user equipment may simultaneously receive or transmit one or multiplecomponent carriers (corresponding to multiple serving cells) dependingon its capabilities. A LTE-A Rel. 10 user equipment with receptionand/or transmission capabilities for carrier aggregation cansimultaneously receive and/or transmit on multiple serving cells,whereas an LTE Rel. 8/9 user equipment can receive and transmit on asingle serving cell only, provided that the structure of the componentcarrier follows the Rel. 8/9 specifications.

Carrier aggregation is supported for both contiguous and non-contiguouscomponent carriers with each component carrier limited to a maximum of110 Resource Blocks in the frequency domain using the 3GPP LTE (Release8/9) numerology.

It is possible to configure a 3GPP LTE-A (Release 10) compatible userequipment to aggregate a different number of component carriersoriginating from the same eNodeB (base station) and of possiblydifferent bandwidths in the uplink and the downlink. The number ofdownlink component carriers that can be configured depends on thedownlink aggregation capability of the UE. Conversely, the number ofuplink component carriers that can be configured depends on the uplinkaggregation capability of the UE. It may not be possible to configure amobile terminal with more uplink component carriers than downlinkcomponent carriers.

In a typical TDD deployment, the number of component carriers and thebandwidth of each component carrier in uplink and downlink is the same.Component carriers originating from the same eNodeB need not to providethe same coverage.

The spacing between centre frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time preserve orthogonality of the subcarriers with15 kHz spacing. Depending on the aggregation scenario, the n*300 kHzspacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO for uplink) at most one transport block per componentcarrier. A transport block and its potential HARQ retransmissions needto be mapped on the same component carrier.

The Layer 2 structure with activated carrier aggregation is shown inFIG. 5 and FIG. 6 for the downlink and uplink respectively.

When carrier aggregation is configured, the mobile terminal only has oneRRC connection with the network. At RRC connectionestablishment/re-establishment, one cell provides the security input(one ECGI, one PCI and one ARFCN) and the non-access stratum mobilityinformation (e.g. TAI) similarly as in LTE Rel. 8/9. After RRCconnection establishment/re-establishment, the component carriercorresponding to that cell is referred to as the downlink Primary Cell(PCell). There is always one and only one downlink PCell (DL PCell) andone uplink PCell (UL PCell) configured per user equipment in connectedstate. Within the configured set of component carriers, other cells arereferred to as Secondary Cells (SCells); with carriers of the SCellbeing the Downlink Secondary Component Carrier (DL SCC) and UplinkSecondary Component Carrier (UL SCC). The characteristics of thedownlink and uplink PCell are:

-   -   For each SCell the usage of uplink resources by the UE, in        addition to the downlink ones is configurable; the number of DL        SCCs configured is therefore always larger or equal to the        number of UL SCCs, and no SCell can be configured for usage of        uplink resources only.    -   The uplink PCell is used for transmission of Layer 1 uplink        control information.    -   The downlink PCell cannot be de-activated, unlike SCells.    -   From UE perspective, each uplink resource only belongs to one        serving cell.    -   The number of serving cells that can be configured depends on        the aggregation capability of the UE.    -   Re-establishment is triggered when the downlink PCell        experiences Rayleigh fading (RLF), not when downlink SCells        experience RLF.    -   The downlink PCell cell can change with handover (i.e. with        security key change and RACH procedure).    -   Non-access stratum information is taken from the downlink PCell.    -   PCell can only be changed with handover procedure (i.e. with        security key change and RACH procedure).    -   PCell is used for transmission of PUCCH.

The configuration and reconfiguration of component carriers can beperformed by RRC. Activation and deactivation is done via MAC controlelements. At intra-LTE handover, RRC can also add, remove, orreconfigure SCells for usage in the target cell. When adding a newSCell, dedicated RRC signaling is used for sending the systeminformation of the SCell, the information being necessary fortransmission/reception (similarly as in Rel-8/9 for handover).

When a user equipment is configured with carrier aggregation there isone pair of uplink and downlink component carriers that is alwaysactive. The downlink component carrier of that pair might be alsoreferred to as “DL anchor carrier”. Same applies also for the uplink.

When carrier aggregation is configured, a user equipment may bescheduled over multiple component carriers simultaneously but at mostone random access procedure shall be ongoing at any time. Cross-carrierscheduling allows the PDCCH of a component carrier to schedule resourceson another component carrier. For this purpose a component carrieridentification field is introduced in the respective DCI formats, calledCIF.

A linking between uplink and downlink component carriers allowsidentifying the uplink component carrier for which the grant applieswhen there is no-cross-carrier scheduling. The linkage of downlinkcomponent carriers to uplink component carrier does not necessarily needto be one to one. In other words, more than one downlink componentcarrier can link to the same uplink component carrier. At the same time,a downlink component carrier can only link to one uplink componentcarrier.

Uplink Access Scheme for LTE

For uplink transmission, power-efficient user-terminal transmission isnecessary to maximize coverage. Single-carrier transmission combinedwith FDMA with dynamic bandwidth allocation has been chosen as theevolved UTRA uplink transmission scheme. The main reason for thepreference for single-carrier transmission is the lower peak-to-averagepower ratio (PAPR), compared to multi-carrier signals (OFDMA), and thecorresponding improved power-amplifier efficiency and assumed improvedcoverage (higher data rates for a given terminal peak power). Duringeach time interval, Node B assigns users a unique time/frequencyresource for transmitting user data, thereby ensuring intra-cellorthogonality. An orthogonal access in the uplink promises increasedspectral efficiency by eliminating intra-cell interference. Interferencedue to multipath propagation is handled at the base station (Node B),aided by insertion of a cyclic prefix in the transmitted signal.

The basic physical resource used for data transmission consists of afrequency resource of size BW_(grant) during one time interval, e.g. asub-frame of 0.5 ms, onto which coded information bits are mapped. Itshould be noted that a sub-frame, also referred to as transmission timeinterval (TTI), is the smallest time interval for user datatransmission. It is however possible to assign a frequency resourceBW_(grant) over a longer time period than one TTI to a user byconcatenation of sub-frames.

UL Scheduling Scheme for LTE

The uplink scheme allows for both scheduled access, i.e. controlled byeNB, and contention-based access.

In case of scheduled access, the UE is allocated a certain frequencyresource for a certain time (i.e. a time/frequency resource) for uplinkdata transmission. However, some time/frequency resources can beallocated for contention-based access. Within these time/frequencyresources, UEs can transmit without first being scheduled. One scenariowhere UE is making a contention-based access is for example the randomaccess, i.e. when UE is performing initial access to a cell or forrequesting uplink resources.

For the scheduled access Node B scheduler assigns a user a uniquefrequency/time resource for uplink data transmission. More specificallythe scheduler determines

-   -   which UE(s) is (are) allowed to transmit,    -   which physical channel resources (frequency),    -   Transport format (Modulation Coding Scheme (MCS)) to be used by        the mobile terminal for transmission

The allocation information is signaled to the UE via a scheduling grant,sent on the L1/L2 control channel. For simplicity reasons this channelis called uplink grant channel in the following. A scheduling grantmessage contains at least information which part of the frequency bandthe UE is allowed to use, the validity period of the grant, and thetransport format the UE has to use for the upcoming uplink transmission.The shortest validity period is one sub-frame. Additional informationmay also be included in the grant message, depending on the selectedscheme. Only “per UE” grants are used to grant the right to transmit onthe UL-SCH (i.e. there are no “per UE per RB” grants). Therefore the UEneeds to distribute the allocated resources among the radio bearersaccording to some rules. Unlike in HSUPA, there is no UE based transportformat selection. The eNB decides the transport format based on someinformation, e.g. reported scheduling information and QoS info, and UEhas to follow the selected transport format. In HSUPA the Node B assignsthe maximum uplink resource, and UE selects accordingly the actualtransport format for the data transmissions.

Since the scheduling of radio resources is the most important functionin a shared channel access network for determining Quality of service,there are a number of requirements that should be fulfilled by the ULscheduling scheme for LTE in order to allow for an efficient QoSmanagement.

-   -   Starvation of low priority services should be avoided.    -   Clear QoS differentiation for radio bearers/services should be        supported by the scheduling scheme.    -   The UL reporting should allow fine granular buffer reports (e.g.        per radio bearer or per radio bearer group) in order to allow        the eNB scheduler to identify for which Radio Bearer/service        data is to be sent.    -   It should be possible to make clear QoS differentiation between        services of different users.    -   It should be possible to provide a minimum bit rate per radio        bearer.

As can be seen from above list one essential aspect of the LTEscheduling scheme is to provide mechanisms with which the operator cancontrol the partitioning of its aggregated cell capacity between theradio bearers of the different QoS classes. The QoS class of a radiobearer is identified by the QoS profile of the corresponding SAE bearersignaled from AGW to eNB as described before. An operator can thenallocate a certain amount of its aggregated cell capacity to theaggregated traffic associated with radio bearers of a certain QoS class.The main goal of employing this class-based approach is to be able todifferentiate the treatment of packets depending on the QoS class theybelong to.

DRX (Discontinuous Reception)

DRX functionality can be configured for RRC_IDLE, in which case the UEuses either the specific or default DRX value (defaultPagingCycle); thedefault is broadcasted in the System Information, and can have values of32, 64, 128 and 256 radio frames. If both specific and default valuesare available, the shorter value of the two is chosen by the UE. The UEneeds to wake up for one paging occasion per DRX cycle, the pagingoccasion being one subframe.

DRX functionality can be also configured for an “RRC_CONNECTED” UE, sothat it does not always need to monitor the downlink channels. In orderto provide reasonable battery consumption of user equipment, 3GPP LTE(Release 8/9) as well as 3GPP LTE-A (Release 10) provides a concept ofdiscontinuous reception (DRX). Technical Standard TS 36.321 (NPL 2)Chapter 5.7 explains the DRX and is incorporated by reference herein.

The following parameters are available to define the DRX UE behavior;i.e. the On-Duration periods at which the mobile node is active, and theperiods where the mobile node is in a DRX mode.

-   -   On duration: duration in downlink sub-frames that the user        equipment, after waking up from DRX, receives and monitors the        PDCCH. If the user equipment successfully decodes a PDCCH, the        user equipment stays awake and starts the inactivity timer;        [1-200 subframes; 16 steps: 1-6, 10-60, 80, 100, 200]    -   DRX inactivity timer: duration in downlink sub-frames that the        user equipment waits to successfully decode a PDCCH, from the        last successful decoding of a PDCCH; when the UE fails to decode        a PDCCH during this period, it re-enters DRX. The user equipment        shall restart the inactivity timer following a single successful        decoding of a PDCCH for a first transmission only (i.e. not for        retransmissions). [1-2560 subframes; 22 steps, 10 spares: 1-6,        8, 10-60, 80, 100-300, 500, 750, 1280, 1920, 2560]    -   DRX Retransmission timer: specifies the number of consecutive        PDCCH subframes where a downlink retransmission is expected by        the UE after the first available retransmission time. [1-33        subframes, 8 steps: 1, 2, 4, 6, 8, 16, 24, 33]    -   DRX short cycle: specifies the periodic repetition of the on        duration followed by a possible period of inactivity for the        short DRX cycle. This parameter is optional. [2-640 subframes;        16 steps: 2, 5, 8, 10, 16, 20, 32, 40, 64, 80, 128, 160, 256,        320, 512, 640]    -   DRX short cycle timer: specifies the number of consecutive        subframes the UE follows the short DRX cycle after the DRX        Inactivity Timer has expired. This parameter is optional. [1-16        subframes]    -   Long DRX Cycle Start offset: specifies the periodic repetition        of the on duration followed by a possible period of inactivity        for the DRX long cycle as well as an offset in subframes when        on-duration starts (determined by formula defined in TS 36.321        section 5.7); [cycle length 10-2560 subframes; 16 steps: 10, 20,        30, 32, 40, 64, 80, 128, 160, 256, 320, 512, 640, 1024, 1280,        2048, 2560; offset is an integer between [0-subframe length of        chosen cycle]]

The total duration that the UE is awake is called “Active time”. TheActive Time includes the on-duration of the DRX cycle, the time UE isperforming continuous reception while the inactivity timer has notexpired and the time UE is performing continuous reception while waitingfor a downlink retransmission after one HRQ RTT. Similarly, for theuplink the UE is awake at the subframes where uplink retransmissiongrants can be received, i.e. every 8 ms after initial uplinktransmission until maximum number of retransmissions is reached. Basedon the above, the minimum active time is of length equal to on-duration,and the maximum is undefined (infinite).

The operation of DRX gives the mobile terminal the opportunity todeactivate the radio circuits repeatedly (according to the currentlyactive DRX cycle) in order to save power. Whether the UE indeed remainsin DRX (i.e. is not active) during the DRX period may be decided by theUE; for example, the UE usually performs inter-frequency measurementswhich cannot be conducted during the On-Duration, and thus need to beperformed some other time, during the DRX opportunity of time.

The parameterization of the DRX cycle involves a trade-off betweenbattery saving and latency. For example, in case of a web browsingservice, it is usually a waste of resources for a UE to continuouslyreceive downlink channels while the user is reading a downloaded webpage. On the one hand, a long DRX period is beneficial for lengtheningthe UE's battery life. On the other hand, a short DRX period is betterfor faster response when data transfer is resumed—for example when auser requests another web page.

To meet these conflicting requirements, two DRX cycles—a short cycle anda long cycle—can be configured for each UE; the short DRX cycle isoptional, i.e. only the long DRX cycle is used. The transition betweenthe short DRX cycle, the long DRX cycle and continuous reception iscontrolled either by a timer or by explicit commands from the eNodeB. Insome sense, the short DRX cycle can be considered as a confirmationperiod in case a late packet arrives, before the UE enters the long DRXcycle. If data arrives at the eNodeB while the UE is in the short DRXcycle, the data is scheduled for transmission at the next on-durationtime, and the UE then resumes continuous reception. On the other hand,if no data arrives at the eNodeB during the short DRX cycle, the UEenters the long DRX cycle, assuming that the packet activity is finishedfor the time being.

During the Active Time the UE monitors PDCCH, reports SRS (SoundingReference Signal) as configured and reports CQI (Channel QualityInformation)/PMI (Precoding Matrix Indicator)/RI (Rank Indicator)/PTI(Precoder Type Indication) on PUCCH. When UE is not in Active time,type-O-triggered SRS and CQI/PMI/RI/PTI on PUCCH may not be reported. IfCQI masking is set up for the UE, the reporting of CQI/PMI/RI/PTI onPUCCH is limited to On Duration.

Available DRX values are controlled by the network and start fromnon-DRX up to x seconds. Value x may be as long as the paging DRX usedin RRC_IDLE. Measurement requirements and reporting criteria can differaccording to the length of the DRX interval, i.e. long DRX intervals mayhave more relaxed requirements (for more details see further below).When DRX is configured, periodic CQI reports can only be sent by the UEduring “active-time”. RRC can further restrict periodic CQI reports sothat they are only sent during the on-duration.

FIG. 7 discloses an example of DRX. The UE checks for schedulingmessages (indicated by its C-RNTI, cell radio network temporaryidentity, on the PDCCH) during the “on duration” period of either thelong DRX cycle or the short DRX cycle depending on the currently activecycle. When a scheduling message is received during an “on duration”,the UE starts an “inactivity timer” and monitors the PDCCH in everysubframe while the Inactivity Timer is running During this period, theUE can be regarded as being in a continuous reception mode. Whenever ascheduling message is received while the Inactivity Timer is running,the UE restarts the Inactivity Timer, and when it expires the UE movesinto a short DRX cycle and starts a “short DRX cycle timer”. The shortDRX cycle may also be initiated by means of a MAC Control Element. Whenthe short DRX cycle timer expires, the UE moves into a long DRX cycle.

In addition to this DRX behaviour, a “HARQ Round Trip Time (RTT) timer”is defined with the aim of allowing the UE to sleep during the HARQ RTT.When decoding of a downlink transport block for one HARQ process fails,the UE can assume that the next retransmission of the transport blockwill occur after at least “HARQ RTT” subframes. While the HARQ RTT timeris running, the UE does not need to monitor the PDCCH. At the expiry ofthe HARQ RTT timer, the UE resumes reception of the PDCCH as normal.

There is only one DRX cycle per user equipment. All aggregated componentcarriers follow this DRX pattern.

Uplink Power Control

Uplink transmission power control in a mobile communication systemserves an important purpose: it balances the need for sufficienttransmitted energy per bit to achieve the required Quality of Service(QoS) against the need to minimize interference to other users of thesystem and to maximize the battery life of the mobile terminal. Inachieving this purpose, the role of the Power Control (PC) becomesdecisive to provide the required SINR while controlling at the same timethe interference caused to neighbouring cells. The idea of classic PCschemes in uplink is that all users are received with the same SINR,which is known as full compensation. As an alternative, the 3GPP hasadopted for LTE the use of Fractional Power Control (FPC). This newfunctionality makes users with a higher path-loss operate at a lowerSINR requirement so that they will more likely generate lessinterference to neighboring cells.

Detailed power control formulae are specified in LTE for the PhysicalUplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH)and the Sounding Reference Signals (SRSs) (for further details on thepower control formulae, see for example 3GPP TS 36.213, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical layer procedures(Release 8)”, version 8.8.0 (NPL 3) or 9.1.0, section 5.1, available athttp://www.3gpp.org and incorporated herein by reference). The formulafor each of these uplink signals follows the same basic principles; inall cases they can be considered as a summation of two main terms: abasic open-loop operating point derived from static or semi-staticparameters signaled by the eNodeB, and a dynamic offset updated fromsubframe to subframe.

The basic open-loop operating point for the transmit power per resourceblock depends on a number of factors including the inter-cellinterference and cell load. It can be further broken down into twocomponents, a semi-static base level P₀, further comprised of a commonpower level for all user equipments in the cell (measured in dBm) and aUE-specific offset, and an open-loop path-loss compensation component.The dynamic offset part of the power per resource block can also befurther broken down into two components, a component dependent on theMCS and explicit Transmitter Power Control (TPC) commands.

The MCS-dependent component (referred to in the LTE specifications asΔ_(TF)

where TF stands for “Transport Format”) allows the transmitted power perresource block to be adapted according to the transmitted informationdata rate.

The other component of the dynamic offset is the UE-specific TPCcommands. These can operate in two different modes: accumulative TPCcommands (available for PUSCH, PUCCH and SRS) and absolute TPC commands(available for PUSCH only). For the PUSCH, the switch between these twomodes is configured semi-statically for each UE by RRC signaling, i.e.the mode cannot be changed dynamically. With the accumulative TPCcommands, each TPC command signals a power step relative to the previouslevel.

Power Headroom Reporting

In order to assist the eNodeB to schedule the uplink transmissionresources to different user equipments in an appropriate way, it isimportant that the user equipment can report its available powerheadroom to eNodeB.

The eNodeB can use the power headroom reports to determine how much moreuplink bandwidth per sub-frame a user equipment is capable of using.This helps to avoid allocating uplink transmission resources to userequipments which are unable to use them in order to avoid a waste ofresources.

The range of the power headroom report is from +40 to −23 dB (see 3GPPTS 36.133, “Requirements for support of radio resource management”,version 8.7.0 (NPL 4), section 9.1.8.4, available at http//www.3gpp.organd incorporated in its entirety herein by reference). The negative partof the range enables the user equipment to signal to the eNodeB theextent to which it has received an UL grant which would require moretransmission power than the UE has available. This would enable theeNodeB to reduce the size of a subsequent grant, thus freeing uptransmission resources to allocate to other UEs.

A power headroom report can only be sent in sub-frames in which a UE hasan UL transmission grant. The report relates to the sub-frame in whichit is sent. The headroom report is therefore a prediction rather than adirect measurement; the UE cannot directly measure its actualtransmission power headroom for the sub-frame in which the report is tobe transmitted. It therefore relies on reasonably accurate calibrationof the UE's power amplifier output.

A number of criteria are defined to trigger a power headroom report.These include:

-   -   A significant change in estimated path loss since the last power        headroom report    -   More than a configured time has elapsed since the previous power        headroom report    -   More than a configured number of closed-loop TPC commands have        been implemented by the UE

The eNodeB can configure parameters to control each of these triggersdepending on the system loading and the requirements of its schedulingalgorithm. To be more specific, RRC controls power headroom reporting byconfiguring the two timers “periodicPHR-Timer” and “prohibitPHR-Timer”,and by signalling “dl-PathlossChange” which sets the change in measureddownlink pathloss to trigger a power headroom report.

The power headroom report is send as a MAC Control Element. It consistsof a single octet where the two highest bits are reserved and the sixlowest bits represent the 64 dB values mentioned above in 1 dB steps.The structure of the MAC Control Element for the Rel-8 power headroomreport is shown in FIG. 8.

The UE power headroom PH [dB] valid for sub-frame i is defined by thefollowing equation (see section 5.1.1.2 of 3GPP TS 36.213):PH(i)=P _(CMAX)−{10·log₁₀(M _(PUSCH)(i))+P ₀ _(_) _(PUSCH)(j)+a(j)·PL+Δ_(TF)(i)+f(i)}   (Equation 1)

The power headroom is rounded to the closest value in the range [40;−23] dB with steps of 1 dB. P_(CMAX) is the total maximum UE transmitpower (or total maximum transmit power of the user equipment) and is avalue chosen by the user equipment in the given range of P_(CMAX) _(_)_(L) and P_(CMAX) _(_) _(H) based on the following constraints:P _(CMAX) _(_) _(L) ≤P _(CMAX) ≤P _(CMAX) _(_) _(H)P _(CMAX) _(_) _(L)=min(P _(EMAX) −ΔT _(c) ,P _(PowerClass)−MPR−AMPR−ΔT_(c))P _(CMAX) _(_) _(H)=min(P _(EMAX) ,P _(PowerClass))P_(EMAX) is the value signaled by the network, and MPR, AMPR (alsodenoted as A-MPR) andΔT _(c)are specified in 3GPP TS 36.101, “Evolved Universal Terrestrial RadioAccess (E-UTRA); User Equipment (UE) radio transmission and reception”,version 8.7.0 (NPL 5), section 6.2 available at http//www.3gpp.org andincorporated herein by reference.

MPR is a power reduction value, the so-called Maximum Power Reduction,used to control the Adjacent Channel Leakage Power Ratio (ACLR)associated with the various modulation schemes and the transmissionbandwidth.

A-MPR is the additional maximum power reduction. It is band specific andit is applied when configured by the network. Therefore, P_(CMAX) is UEimplementation specific and hence not known by eNB.

Uplink Power Control for Carrier Aggregation

One main point of UL Power control for LTE-Advance is that a componentcarrier specific UL power control is supported, i.e. there will be oneindependent power control loop for each UL component carrier configuredfor the UE. Furthermore power headroom is reported per componentcarrier.

In Rel-10 within the scope of carrier aggregation there are two maximumpower limits, a maximum total UE transmit power and a CC-specificmaximum transmit power. RAN1 agreed at the RAN1#60bis meeting that apower headroom report, which is reported per CC, accounts for themaximum power reduction (MPR). In other words, the power reductionapplied by the UE is taken into account in the CC-specific maximumtransmission power P_(CMAX,c) (c denotes the component carrier). Asalready mentioned before, the purpose of MPR/A-MPR is to allow themobile device to lower its maximum transmission power in order to beable to meet the requirements on signal quality, spectrum emission maskand spurious emissions.

As already mentioned before the purpose of values MPR/A-MPR is to allowthe mobile device to lower its maximum transmission power in order to beable to meet the requirements on signal quality, spectrum emission maskand spurious emissions.

In addition to MPR and A-MPR in Release 10 the so called powermanagement MPR, also referred to as P-MPR, was introduced in order toaccount for multi-RAT terminals which may have to limit their LTE totaloutput power, particularly when simultaneous transmission on another RATis taking place. Such power restrictions may arise, for example fromregulations on Specific Absorption Rate (SAR) of radio energy into auser's body or from out-of-band emission requirements that may beaffected by the inter-modulation products of the simultaneous radiotransmissions. The P-MPR is not aggregated with MPR/A-MPR, since anyreduction in a UE's maximum output power for the latter factor helps tosatisfy the requirements that would have necessitated P-MPR.

Considering now the additional power management MPR (P-MPR), the UEconfigures its nominal maximum transmission power P_(CMAX), i.e. themaximum transmission power available for the UE, according to thefollowing equations:P _(CMAX) _(_) _(L) ≤P _(CMAX) ≤P _(CMAX) _(_) _(H)P _(CMAX) _(_) _(L)=MIN{P _(EMAX) −ΔT _(c) ,P_(PowerClass)−max(MPR+A-MPR,P-MPR)−ΔT _(c)}P _(CMAX) _(_) _(H)=MIN{P _(EMAX) ,P _(PowerClass)}

For the case of carrier aggregation, the P_(CMAX) becomes P_(CMAX,c) thecomponent-carrier specific maximum transmission power. Essentially theconfigured maximum output power on serving cell c shall be set withinthe following bounds:P _(CMAX) _(_) _(L,c) ≤P _(CMAX,c) ≤P _(CMAX) _(_) _(H,c)

Two different deployments are to be considered, one where aggregatedcarriers are within the same frequency band, and also the case wherecarriers of different frequency bands are aggregated.

For intra-band contiguous carrier aggregation:P _(CMAX) _(_) _(L,c)=MIN{P _(EMAX,c) −ΔT _(C,c) ,P_(PowerClass)−MAX(MPR_(c) +A-MPR_(c) +ΔT _(IB,c) ,P-MPR_(c))−ΔT _(C,c)}

For inter-band carrier aggregation:P _(CMAX) _(_) _(L,c)=MIN{P _(EMAX,c) −ΔT _(C,c) ,P_(PowerClass)−MAX(MPR_(c) +A-MPR_(c) +ΔT _(IB,c) ,P-MPR_(c))−ΔT _(C,c)}P _(CMAX) _(_) _(H,c)=MIN{P _(EMAX,c) ,P _(PowerClass)}

P_(EMAX,c) is the value given by IE P-Max for serving cell c in TS36.331

For inter-band carrier aggregation, MPR_(c) and A-MPR_(c) apply perserving cell c, i.e. there is a separate MPR and A-MPR per serving cell.For intra-band contiguous carrier aggregation, MPR_(c)=MPR, andA-MPR_(c)=A-MPR. P-MPR_(c) accounts for power management for servingcell c. For intra-band contiguous carrier aggregation, there is onepower management term for the UE, P-MPR, and P-MPR_(c)=P-MPR.

For carrier aggregation with two UL serving cells, the total configuredmaximum output power P_(CMAX) shall be set within the following bounds:P _(CMAX) _(_) _(L) _(_) _(CA) ≤P _(CMAX) ≤P _(CMAX) _(_) _(H) _(_)_(CA)For intra-band contiguous carrier aggregation,P _(CMAX) _(_) _(L) _(_) _(CA)=MIN{10·log₁₀ Σp _(EMAX,c) −ΔT _(C) ,P_(PowerClass)−MAX(MPR+A-MPR+ΔT _(IB,c) ,P-MPR)−ΔT _(C)}P _(CMAX) _(_) _(H) _(_) _(CA)=MIN{10·log₁₀ Σp _(EMAX,c) ,P_(PowerClass)}where p_(EMAX,c) is the linear value of P_(EMAX,c) which is given by RRCsignalling (for details see TS 36.331 incorporated herein by reference).

For inter-band carrier aggregation with up to one serving cell c peroperating band:P _(CMAX) _(_) _(L) _(_) _(CA)=MIN{10·log₁₀ΣMIN[p _(EMAX,c)/(Δt_(C,c)),p _(PowerClass)/(mpr_(c)-a-mpr_(c)-Δt _(C,c)-Δt _(IB,c)),p_(PowerClass)/(p-mpr_(c) ·Δt _(C,c))],P _(PowerClass)}P _(CMAX) _(_) _(H) _(_) _(CA)=MIN{10·log₁₀ Σp _(EMAX,c) ,P_(PowerClass)}where p_(EMAX,c) is the linear value of P_(EMAX,c) which is given by TS36.331. MPR_(c) and A-MPR_(c) apply per serving cell c and are specifiedin subclause 6.2.3 and subclause 6.2.4 of TS36.101, respectively, alsoincorporated herein by reference. mpr_(c) is the linear value ofMPR_(c). a-mpr_(c) is the linear value of A-MPR_(c). P-MPR_(c) accountsfor power management for serving cell c. p-mpr_(c) is the linear valueof P-MPR_(c).

Further information about the definition of CC-specific maximumtransmission power respectively the UE total maximum transmission powercan be found in TS36.101, incorporated herein by reference.

Different to Rel-8/9 for LTE-A the UE has also to cope with simultaneousPUSCH-PUCCH transmission, multi-cluster scheduling, and simultaneoustransmission on multiple CCs, which requires larger MPR values and alsocauses a larger variation of the applied MPR values compared to Rel-8/9.

It should be noted that the eNB does not have knowledge of the powerreduction applied by the UE on each CC, since the actual power reductiondepends on the type of allocation, the standardized MPR value and alsoon the UE implementation. Therefore, the eNB does not know theCC-specific maximum transmission power relative to which the UEcalculates the PHR. In Rel-8/9 for example UE's maximum transmit powerP_(CMAX) can be within some certain range as described above.P _(CMAX) _(_) _(L) ≤P _(CMAX) ≤P _(CMAX) _(_) _(H)

Due to the fact that the power reduction applied by the UE to themaximum transmit power of a CC is not known by eNB it was agreed tointroduce in Rel-10 a new power headroom MAC control element, which isalso referred to as extended power headroom MAC control element. Themain difference to the Rel-8/9 PHR MAC CE format, is that it includes aRel-8/9 power headroom value for each activated UL CC and is hence ofvariable size. Furthermore it not only reports the power headroom valuefor a CC but also the corresponding P_(CMAX,c) (maximum transmit powerof CC with the index c) value. In order to account for simultaneousPUSCH-PUCCH transmissions, UE reports for PCell the Rel-8/9 powerheadroom value which is related to PUSCH only transmissions (referred totype 1 power headroom) and if the UE is configured for simultaneousPUSCH-PUCCH transmission, a further Power headroom value, whichconsiders PUCCH and PUSCH transmissions, also referred to as type 2power headroom.

In order to be able to distinguish at the eNB side whether the maximumtransmission power was reduced due to MPR/A-MPR power reduction orcaused by applying a P-MPR, a one bit indicator, also referred to asP-bit, was introduced in the extended power headroom MAC CE. More inparticular the UE sets P=1 if the corresponding maximum transmissionpower (P_(CMAX,c)) would have had a different value if no power backoffdue to power management (P-MPR) had been applied. Essentially this P bitis used by the eNB to remove the PHR reports, which are affected byP-MPR, from the MPR-learning algorithm in the eNB, i.e. eNB stores in aninternal table which MPR value the UE uses for certain resourceallocations.

For further details on the extended power headroom MAC Control elementillustrated in FIG. 9, see for example 3GPP TS 36.321, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC)protocol specification (Release 10)”, version 10.0.0 (NPL 2), section6.1.3.6a, available at http://www.3gpp.org and incorporated herein byreference.

Type-1 power headroom can also be reported for subframes where there isno actual PUSCH transmission. This special PHR is also referred to asvirtual PHR. In such cases, 10 log₁₀(M_(PUSCH)(i)) andΔ_(TF,c)(i)

in the expression of the power headroom report shown above are set tozero. Values for the pathloss (PL), received TPC commands f(i) and otherCC specific constants (P₀ _(_) _(PUSCH)(j), a) are available for the ULCC, even without UL data transmission:PH _(virtual,c)(i)=P _(CMAX,H,c) −{P ₀ _(_) _(PUSCH)(j)+a(j)+PL _(c)+f(i)}

This can be seen as the power headroom assuming a default transmissionconfiguration corresponding to the minimum possible resource assignment(M=1) and the modulation-and-coding scheme associated withΔ_(TF,c)(i)=0 dB.

The carrier-specific maximum transmission power{tilde over (P)} _(CMAX,c)(i)

is computed assuming

MPR=0 dB

A-MPR=0 dB

P-MPR=0 dB

ΔT_(c)=0 dB.

Essentially,{tilde over (P)} _(CMAX,c)(i)

is equal to P_(CMAX) _(_) _(H,c)=MIN{P_(EMAX,c), P_(PowerClass)}.

Similar to Type-1 power headroom reporting, the Type-2 power headroomcan also be reported for subframes in which no PUSCH and/or PUCCH istransmitted. In that case a virtual PUSCH and/or PUCCH transmit power iscalculated, assuming the smallest possible resource assignment (M=1) andΔMCS=0 dBfor PUSCH andh(n _(CQI) ,nH _(ARQ) ,n _(SR)),Δ_(F) _(_) _(PUCCH)(F),Δ_(TxD)(F′)set to 0 for PUCCH. Further details about the computation of powerheadroom can be found in TS36.213, incorporated herein by reference.

Small Cells

Explosive demands for mobile data are driving changes in how mobileoperators will need to respond to the challenging requirements of highercapacity and improved Quality of user Experience (QoE). Currently,fourth generation wireless access systems using Long Term Evolution(LTE) are being deployed by many operators worldwide in order to offerfaster access with lower latency and more efficiency than 3G/3.5Gsystem. Nevertheless, the anticipated future traffic growth is sotremendous that there is a vastly increased need for further networkdensification to handle the capacity requirements, particularly in hightraffic areas (hot spot areas) that generate the highest volume oftraffic. Network densification—increasing the number of network nodes,thereby bringing them physically closer to the user terminals—is a keyto improving traffic capacity and extending the achievable user-datarates of a wireless communication system.

In addition to straightforward densification of a macro deployment,network densification can be achieved by the deployment of complementarylow-power nodes respectively small cells under the coverage of anexisting macro-node layer. In such a heterogeneous deployment, thelow-power nodes provide very high traffic capacity and very high userthroughput locally, for example in indoor and outdoor hotspot positions.Meanwhile, the macro layer ensures service availability and QoE over theentire coverage area. In other words, the layer containing the low-powernodes can also be referred to as providing local-area access, incontrast to the wide-area-covering macro layer.

The installation of low-power nodes respectively small cells as well asheterogeneous deployments has been possible since the first release ofLTE. In this regard, a number of solutions have been specified in recentreleases of LTE (i.e., Release-10/11). More specifically, these releasesintroduced additional tools to handle inter-layer interference inheterogeneous deployments. In order to further optimize performance andprovide cost/energy-efficient operation, small cells require furtherenhancements and in many cases need to interact with or complementexisting macro cells. Such solutions will be investigated during thefurther evolution of LTE-Release 12 and beyond. In particular furtherenhancements related to low-power nodes and heterogeneous deploymentswill be considered under the umbrella of the new Rel-12 study item (SI)“Study on Small Cell Enhancements for E-UTRA and E-UTRAN”. Some of theseactivities will focus on achieving an even higher degree of interworkingbetween the macro and low-power layers, including different forms ofmacro assistance to the low-power layer and dual-layer connectivity.Dual connectivity implies that the device has simultaneous connectionsto both macro and low-power layers.

Some deployment scenarios assumed in this study item on small cellenhancements will be discussed below. In the following scenarios, thebackhaul technologies categorized as non-ideal backhaul in TR 36.932 areassumed.

Both ideal backhaul (i.e., very high throughput and very low latencybackhaul such as dedicated point-to-point connection using opticalfiber) and non-ideal backhaul (i.e., typical backhaul widely used in themarket such as xDSL, microwave, and other backhauls like relaying)should be studied. The performance-cost trade-off should be taken intoaccount.

A categorization of non-ideal backhaul based on operator inputs islisted in the table below:

TABLE 1 Priority Backhaul Latency (1 is the Technology (One way)Throughput highest) Fiber Access 1 10-30 ms 10 M-10 Gbps 1 Fiber Access2  5-10 ms 100-1000 Mbps 2 Fiber Access 3  2-5 ms 50 M-10 Gbps 1 DSLAccess 15-60 ms  10-100 Mbps 1 Cable 25-35 ms  10-100 Mbps 2 Wireless 5-35 ms 10 Mbps-100 Mbps typical, 1 Backhaul maybe up to Gbps range

Fiber access which can be used to deploy Remote Radio Heads (RRHs) isnot assumed in this study. HeNBs are not precluded, but notdistinguished from Pico eNBs in terms of deployment scenarios andchallenges even though the transmission power of HeNBs is lower thanthat of Pico eNBs. The following 3 scenarios are considered.

Scenario #1 is illustrated in FIG. 10 and is the deployment scenariowhere macro and small cells on the same carrier frequency(intra-frequency) are connected via a non-ideal backhaul. User aredistributed both for outdoor and indoor.

Scenario #2 is illustrated in FIGS. 11 and 12 and refers to a deploymentscenario where macro and small cells on different carrier frequencies(inter-frequency) are connected via a non-ideal backhaul. User aredistributed both for outdoor and indoor. There are essentially twodifferent scenarios #2, referred herein as 2a and 2b, the differencebeing that in scenario 2b an indoor small cell deployment is considered.

Scenario #3 is illustrated in FIG. 13 and refers to a deploymentscenario where only small cells on one or more carrier frequencies areconnected via a non-ideal backhaul link.

Depending on the deployment scenario, different challenges/problemsexist which need to be further investigated. During the study item phasesuch challenges have been identified for the corresponding deploymentscenarios and captured in TS 36.842; more details on thosechallenges/problems can be found there.

In order to resolve the identified challenges which are described insection 5 of TS36.842, the following design goals are taken into accountfor this study in addition to the requirements specified in TR 36.932.

In terms of mobility robustness:

-   -   For UEs in RRC_CONNECTED, Mobility performance achieved by small        cell deployments should be comparable with that of a macro-only        network.

In terms of increased signaling load due to frequent handover:

-   -   Any new solutions should not result in excessive increase of        signaling load towards the Core Network. However, additional        signaling and user plane traffic load caused by small cell        enhancements should also be taken into account.

In terms of improving per-user throughput and system capacity:

-   -   Utilising radio resources across macro and small cells in order        to achieve per-user throughput and system capacity similar to        ideal backhaul deployments while taking into account QoS        requirements should be targeted.

Dual Connectivity

One promising solution to the problems which are currently underdiscussion in 3GPP RAN working groups is the so-called “dualconnectivity” concept. The term “dual connectivity” is used to refer toan operation where a given UE consumes radio resources provided by atleast two different network nodes connected via a non-ideal backhaul.Essentially, the UE is connected with both a macro cell (macro eNB) andsmall cell (secondary or small eNB). Furthermore, each eNB involved indual connectivity for a UE may assume different roles. Those roles donot necessarily depend on the eNB's power class and can vary among UEs.

Since the study item is currently at a very early stage, details on dualconnectivity are not decided yet. For example the architecture has notbeen agreed on yet. Therefore, many issues/details, e.g. protocolenhancements, are still open currently. FIG. 14 shows an exemplaryarchitecture for dual connectivity. It should be only understood as onepotential option; the present disclosure is not limited to this specificnetwork/protocol architecture but can be applied generally. Thefollowing assumptions on the architecture are made here:

-   -   Per bearer level decision where to serve each packet, C/U plane        split. As an example UE RRC signalling and high QoS data such as        VoLTE can be served by the Macro cell, while best effort data is        offloaded to the small cell.    -   No coupling between bearers, so no common PDCP or RLC required        between the Macro cell and small cell.    -   Looser coordination between RAN nodes.    -   SeNB has no connection to S-GW, i.e. packets are forwarded by        MeNB.    -   Small Cell is transparent to CN.

Regarding the last two bullet points, it should be noted that it's alsopossible that SeNB is connected directly with the S-GW, i.e. S1-U isbetween S-GW and SeNB. Essentially, there are three different optionsw.r.t. the bearer mapping/splitting:

-   -   Option 1: S1-U also terminates in SeNB; depicted in FIG. 15a    -   Option 2: S1-U terminates in MeNB, no bearer split in RAN;        depicted in FIG. 15b    -   Option 3: S1-U terminates in MeNB, bearer split in RAN; depicted        in FIG. 15c

FIGS. 15a-c depict those three options taking the downlink direction forthe U-Plane data as an example. For explanation purposes, option 2 ismainly assumed for this application, and is the basis for FIG. 14 too.

In addition to the discussion on the splitting of the U-plane data asdepicted in FIGS. 15a-c , different alternatives have been discussed forthe user plane architecture too.

A common understanding is that, when the S1-U interface terminates atthe MeNB (FIG. 15b,c ), the protocol stack in the SeNB must at leastsupport RLC (re-)segmentation. This is due to the fact that RLC(re-)segmentation is an operation that is tightly coupled to thephysical interface (e.g. MAC layer indicating size of the RLC PDU, seeabove), and when a non-ideal backhaul is used, RLC (re-)segmentationmust take place in the same node as the one transmitting the RLC PDUs.

Shortcomings of Prior Art Power Control

As explained in the previous sections, small cells and dual connectivityare a recent development and still pose several problems that need to beaddressed in order to allow for an efficient system.

In the dual connectivity scenarios as explained above simultaneousuplink transmissions by the UE to both the MeNB and SeNB (also referredto as dual Tx) are supported for Release 12. There are two independentschedulers, one residing in the MeNB and the other one residing in theSeNB, which each schedule uplink transmission for the UE independentlyfrom one another. More in particular, uplink resource allocationsscheduled in one cell are not known in the other cell. In other words,the MeNB scheduler is not aware of uplink scheduling decisions made bythe SeNB, and vice versa.

For said reason, there is an increased probability that the UE will bepower limited, i.e. that the UE total maximum transmission power isexceeded when two uplink transmission are scheduled with too much power.

This is illustrated in FIG. 16, which shows a power-limited situationwhere two uplink transmissions are scheduled for the UE, one to the MeNBand one to the SeNB. As apparent therefrom, the simultaneous uplinktransmissions exceed to the total maximum UE transmit power, for whichreasons power scaling is performed by the UE for the uplinktransmissions so as to keep the total power used for the twotransmissions below the total maximum UE transmit power. Power scalingin turn reduces the scheduling efficiency and performance.

CITATION LIST Non Patent Literature

-   NPL 1: 3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access    (E-UTRA); Physical Channels and Modulation”, version 8.9.0-   NPL 2: 3GPP TS 36.321, “Evolved Universal Terrestrial Radio Access    (E-UTRA); Medium Access Control (MAC) protocol specification”,    version 10.0.0-   NPL 3: 3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access    (E-UTRA); Physical layer procedures”, version 8.8.0-   NPL 4: 3GPP TS 36.133, “Requirements for support of radio resource    management”, version 8.7.0-   NPL 5: 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access    (E-UTRA); User Equipment (UE) radio transmission and reception”,    version 8.7.0

SUMMARY

One non-limiting and exemplary embodiment provides an improved methodfor power control in a mobile communication system with a mobile stationin dual connectivity with a master and secondary base station, avoidingthe problems of the prior art as identified above. Another exemplaryembodiment provides the power headroom reporting so as to assist in theimproved power control for dual connectivity scenarios.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and Figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

In one general aspect, the techniques disclosed here feature a methodfor power headroom reporting in a mobile communication system, wherein amobile station is connected via a first radio link to a master basestation and at least to one secondary base station via a secondary radiolink, the method comprising the steps of: calculating by the mobilestation a first power headroom report for the first radio link betweenthe mobile station and the master base station, transmitting thecalculated first power headroom report together with informationallowing the master base station to determine information on thepathloss of the secondary radio link between the mobile station and thesecondary base station, from the mobile station to the master basestation, and calculating by the mobile station a secondary powerheadroom report for the secondary radio link between the mobile stationand the secondary base station, and transmitting the calculatedsecondary power headroom report from the mobile station to the secondarybase station.

The general aspect may be implemented using a system, a device, and acomputer program, and any combination of systems, devices, and computerprograms.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an exemplary architecture of a 3GPP LTE system.

FIG. 2 shows an exemplary overview of the overall E-UTRAN architectureof 3GPP LTE.

FIG. 3 shows exemplary subframe boundaries on a downlink componentcarrier as defined for 3GPP LTE (Release 8/9).

FIG. 4 shows an exemplary downlink resource grid of a downlink slot asdefined for 3GPP LTE (Release 8/9).

FIG. 5 shows the 3GPP LTE-A (Release 10) Layer 2 structure withactivated carrier aggregation for the downlink.

FIG. 6 shows the 3GPP LTE-A (Release 10) Layer 2 structure withactivated carrier aggregation for the uplink.

FIG. 7 illustrates a DRX operation of a mobile terminal and inparticular the DRX opportunity, on-duration, according to the short andlong DRX cycle.

FIG. 8 shows a Power Headroom Report, PHR, MAC control element asdefined in 3GPP LTE (Release 8/9).

FIG. 9 illustrates an extended Power Headroom Report, ePHR, MAC controlelement as defined in 3GPP LTE (Release 10).

FIG. 10 illustrates a deployment scenario for small cell enhancement,where macro and small cells are on the same carrier frequency.

FIG. 11 illustrates further deployment scenarios for small cellenhancement where macro and small cells are on different carrierfrequencies, the small cell being outdoor.

FIG. 12 illustrates further deployment scenarios for small cellenhancement where macro and small cells are on different carrierfrequencies, the small cell being indoor.

FIG. 13 illustrates a further deployment scenario for small cellenhancement with only small cells.

FIG. 14 gives an overview of the communication system architecture fordual connectivity with macro and small eNBs connected to the corenetwork, where the S1-U interface terminates in the Macro eNB and nobearer splitting is done in RAN.

FIGS. 15a-c illustrate the different options for having two separate EPSbearers between the SGW and the UE.

FIG. 16 illustrates a power-limited scenario of the prior art when theUE is connected to both a MeNB and SeNB, which in turn independentlywould control the output power of the UE for uplink transmission to theMeNB and SeNB.

FIG. 17 illustrates the exchange of initial values of power parametersP_(EMAX,MeNB) and P_(EMAX, SeNB) to from the MeNB to the SeNB and UE,according to one alternative implementation.

FIG. 18 illustrates the exchange of initial values of power parametersP_(EMAX,MeNB) and P_(EMAX,SeNB) to from the MeNB to the SeNB and UE,according to another alternative implementation.

FIG. 19 illustrates the exchange of initial values of power parametersP_(EMAX,MeNB) and P_(EMAX,SeNB) to from the MeNB to the SeNB and UE,according to still another alternative implementation.

FIG. 20 illustrates the structure of a MAC CE for a power headroomreport according to one implementation of the present disclosure usedfor informing the SeNB about the virtual P_(CMAX,SeNB) which isidentical as the P_(EMAX,SeNB), where the extended power headroom reportfor the secondary radio link is supplemented with a virtual powerheadroom report for the secondary report link and with the virtualP_(CMAX,SeNB).

FIG. 21 illustrates the adapted power headroom reporting as performed bythe UE according to an implementation of the present disclosure, wherean extended power headroom report for the secondary radio link istransmitted to the SeNB, and the extended power headroom report for thefirst radio link is supplemented with a virtual power headroom reportfor the secondary radio link so as to inform the MeNB about the pathlossof the secondary radio link.

FIG. 22 illustrates the structure of a MAC CE for a power headroomreport according to one implementation of the present disclosure, whichcan be used in connected with the PHR exchange of FIG. 21, namelyincluding the extended power headroom report for the first radio linkand a virtual power headroom report for the secondary radio link.

FIG. 23 illustrates the structure of a MAC CE for a power headroomreport for the secondary radio link, which can be used in connectionwith the PHR exchange of FIG. 21, namely including the extended powerheadroom report the for the secondary radio link.

DESCRIPTION OF EMBODIMENTS

It is assumed that the mobile station is in dual connectivity and thusconnected to both a master base station and a secondary base station viarespective radio links. As explained above, one of the problems inconnection with the assumed scenario is the two schedulers in the masterand secondary base station, which independently schedule uplinktransmissions for the mobile station. This further includes that themaster and secondary base station also control independently the powerthe mobile station shall use for the respective uplink transmissions. Inorder to avoid power-limited situations as shown exemplarily in FIG. 16,i.e. where the mobile station needs to perform power scaling so as toreduce power output to be within its power output limits, the presentdisclosure suggests as follows.

According to a first aspect of the present disclosure, the power controlfor the mobile station is mainly controlled by a single base station, beit the master base station or the secondary base station. In thefollowing, for illustration purposes only, it is assumed that powercontrol according to the first aspect of the present disclosure, isperformed by the master base station, and not the secondary basestation; of course, the first aspect of the present disclosure alsoapplies with the corresponding necessary changes to a scenario where thesecondary base station is the one controlling the power for the mobilestation.

Consequently, the master base station is responsible for distributingthe available maximum output power of the mobile station for uplinktransmissions between uplink transmissions to the master base stationand uplink transmissions to the secondary base station. The powerdistribution ratio between the two base stations can be defined bytaking into account various parameters of the base stations and theintended communication, such as one or more of the following: pathlosson the radio links from the mobile station to the two base stations,traffic load for the two base stations, resource availability for thetwo radio links to the two base stations etc.

The information on the pathloss can be available at the master basestation e.g. by means of measurement, or by receiving virtual powerheadroom reports (see later). Load information may be directly receivedfrom the secondary base station, or the master base station derives samefrom buffer status reports that are received for the SeNB radio bearersat the master base station.

For example, the power distribution ratio could be: 50% of the maximumoutput power of the mobile station for uplink transmissions to themaster base station, and the other remaining 50% of the maximum outputpower of the mobile station could be determined for uplink transmissionsto the secondary base station. Of course any other power distributionratio is possible as well, e.g. 40/60, 75/25 etc.

Correspondingly, the master base station determines two parameters insaid respect:

1) the maximum output power of the mobile station for uplinktransmissions to the master base station (P_(EMAX,MeNB)) and 2) themaximum output power of the mobile station for uplink transmissions tothe secondary base station (P_(EMAX,SeNB)) These parameters are then tobe used by the mobile station for performing uplink transmissions to therespective base stations.

Upon determination of these parameters, the other entities, i.e. thesecondary base station and the mobile station, are to be informedaccordingly on the parameters; this can be done in many ways, some ofwhich are specified explicitly in the following.

According to a first alternative, the master base station takes care toinform the secondary base station as well as the mobile station aboutthe necessary parameters, including: 1) transmitting the determinedmaximum output power of the mobile station for uplink transmissions tothe secondary base station (P_(EMAX,SeNB)) from the master base stationto the secondary base station, 2) transmitting the determined maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)) from the master base station tothe mobile station, 3) transmitting the determined maximum output powerof the mobile station for uplink transmissions to the master basestation (P_(EMAX,MeNB)) from the master base station to the mobilestation.

According to a second alternative, the master base station transmits,the determined maximum output power of the mobile station for uplinktransmissions to the secondary base station (P_(EMAX,SeNB)), to thesecondary base station, and transmits, the determined maximum outputpower of the mobile station for uplink transmissions to the master basestation (P_(EMAX,MeNB)), to the mobile station. Then, in contrast to thefirst alternative, the secondary base station forwards, the maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)), received from the master basestation, to the mobile station.

According to a further third alternative, the master base stationtransmits both, the determined maximum output power of the mobilestation for uplink transmissions to the secondary base station(P_(EMAX,SeNB)) and the determined maximum output power of the mobilestation for uplink transmissions to the master base station(P_(EMAX,MeNB)), to the mobile station. Then, the mobile stationprovides information, on the determined maximum output power of themobile station for uplink transmissions to the secondary base station(P_(EMAX,SeNB)), to the secondary base station; this in turn can be donein various ways, e.g. as a separate parameter in connection with a powerheadroom report relating to the secondary radio link, or as part of avirtual power headroom report relating to the secondary radio link (moredetails below).

In any case, the two base stations as well as the mobile station get theinformation on the power distribution and thus can perform power controlwith a minimized risk of power limitation since the uplink schedulingand power control should be performed by the base stations in such a waythat the maximum possible output power of the mobile station is notexceeded.

According to further improvements relating to this first aspect, thepower distribution ratio, as initially defined by the master basestation, shall be monitored and then updated (if necessary). The masterbase station, responsible for the power distribution control, isprovided, among others by the mobile station, with the informationnecessary in said respect. As already mentioned above, one criterionbased on which the master base station determines the power distributionratio is the information on the pathloss on the respective radio linksbetween the mobile station and the master/secondary base stations.Correspondingly, the mobile station assists the master base station forthe updating of the power distribution ratio by providing appropriateinformation on the pathloss to the master base station.

First of all, the information on the pathloss on the first radio linkbetween the mobile station and the master base station, can bedetermined by the master base station from usual power headroom reportsrelating to this first radio link, received from the mobile station; thepower headroom value within the power headroom report is calculated bythe mobile station based on the information on the pathloss on the firstradio link to the master base station, and thus the master base stationcan derive this information on the pathloss on the first radio link fromthe received power headroom value. Furthermore pathloss information canbe also derived from mobility measurement reports, i.e. RSRP/RSRQmeasurements, for the first radio link provided to the master basestation.

Furthermore, the master base station shall be provided withcorresponding information on the pathloss on the secondary radio linkbetween the mobile station and the secondary base station. The followingshould be noted in said respect. The power headroom report transmittedby the mobile station to the secondary base station, for the secondaryradio link between the mobile station and the secondary base station,allows the secondary base station to determine the information on thepathloss on the secondary radio link, however would not allow the masterbase station to do the same, since the master base station, unlike thesecondary base station, does not know the resource assignment based onwhich the mobile station calculated the corresponding power headroomreport.

On the other hand, the virtual power headroom report for the secondaryradio link, being calculated by the mobile station based on apre-configured virtual uplink resource assignment for said secondaryradio link to the secondary base station (the uplink resource assignmentbeing pre-determined and thus also known to the master base station),would allow the master base station to determine the information on thepathloss for the secondary radio link.

Therefore, according to one improvement of the first aspect, instead ofdirectly transmitting the information on the pathloss from the mobilestation to the master base station, the mobile station assists themaster base station to determine and update the power distribution bycalculating a virtual power headroom report for the secondary radio linkand by transmitting same to the master base station. Preferably, thesecondary virtual power headroom report (i.e. for the secondary radiolink) is transmitted from the mobile station to the master base station,together with a “normal” power headroom report for the first radio linkbetween the mobile station and the master base station.

Correspondingly, according to this improvement of the first aspect ofthe present disclosure, the power headroom reporting performed by themobile station is adapted such that the mobile station performs thepower headroom reporting for the first and secondary radio links in theusual manner (i.e. power headroom report on first radio link to masterbase station, and power headroom report on secondary radio link tosecondary base station), but in addition, the mobile station calculatesa virtual power headroom report for the secondary radio link andtransmits same, together (i.e. in the same message) with the “usual”power headroom report for the first radio link, to the master basestation.

In the above, when referring to the “power headroom report” for thesecondary or first radio link, preferably the extended power headroomreport is meant, which in addition to the power headroom value comprisesa cell-specific maximum output power, configured by the mobile stationfor uplink transmissions from the mobile station to the master/secondarybase station (P_(CMAX,MeNB/SeNB)), similar to P_(CMAX,c) as defined by3GPP and introduced in the background section.

As a result, the master base station is provided with the necessaryinformation on the pathloss on both radio links and can thus adapt thepower distribution ratio to the changing pathloss situations. The masterbase station can then decide to apply or not apply the updated powerdistribution ratio, i.e. to re-configure the power distribution ratio,by distributing the updated values for the maximum output power of themobile station for uplink transmissions to the master and secondary basestations (P_(EMAX,MeNB))/(P_(EMAX,SeNB)) according to any one of theabove-discussed alternatives. In any case, the secondary base station aswell as the mobile station are provided with and adopt the updatedvalues and can thus perform uplink scheduling and uplink transmissionsaccording to these new updated values of the maximum output powers.

Above, the update of the power distribution ratio by the master basestation has been mainly discussed with regard to a pathloss change andhow the mobile station can assist the master base station in saidrespect by providing information on the pathloss (change) to the masterbase station in one way or another.

According to a second aspect of the present disclosure, the mobilestation is extended with additional functionality to assist the masterbase station with regard to updating the power distribution for othercases as well, such as for the case where the radio link in the uplinkwill not be used (e.g. for a particular minimum length in time) or wherea radio link (in the uplink) is broken. In both cases, it isadvantageous if the power distribution is updated such that the powerassigned to the radio link, not being used in the uplink or beingbroken, is rather used by the other radio link. This will be explainedin detail in the following.

The main idea is that the mobile station determines when a radio link(be it the first or secondary radio link) is becoming inactive or broken(i.e. radio link failure), and then informs the other base stationthereof, such that the power distribution ratio can be updated in amanner that the full power available for the mobile station is assignedto uplink transmissions to the other base station (over the working orused uplink radio link).

In more detail, the mobile station determines when the first radio linkis becoming inactive, which means that the mobile station expects itwill not transmit data in the uplink to the master base station for aparticular time; which can be the case e.g. where the mobile stationenters a discontinuous reception/transmission mode (DRX/DTX) for thisfirst radio link. In this case, the secondary base station is informedabout the first radio link becoming inactive, where in turn thesecondary base station can determine an updated value for the maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)), in particular the full maximumoutput power (since no power is needed for the uplink transmissions onthe other radio link being inactive). This updated value can then betransmitted to the mobile station, such that the mobile station adoptsand uses the updated value for its maximum output power for uplinktransmissions to the secondary base station.

Similarly, the mobile determines when the secondary radio link isbecoming inactive, which means that the mobile station expects it willnot transmit data in the uplink to the secondary base station for aparticular time; which can be the case e.g. where the mobile stationenters a discontinuous reception/transmission mode (DRX/DTX) for thissecondary radio link. In this particular case, the master base stationis informed about the secondary radio link becoming inactive; where inturn the master base station can determine an updated value for themaximum output power of the mobile station for uplink transmissions tothe master base station (P_(EMAX,MeNB)), in particular the full maximumoutput power (since no power is needed for uplink transmissions on theother radio link being inactive). This updated value can then betransmitted to the mobile station, such that the mobile station adoptsand uses the updated value for its maximum output power for uplinktransmissions to the master base station.

In order to inform the master/secondary base station on thesecondary/first radio link becoming inactive as explained above, thereare several options, some of which will be specified below.

When the mobile station determines that the secondary radio link becomesinactive for the uplink, it can prepare a first power headroom reportfor the first radio link between the mobile station and the master basestation, it can set a pre-determined flag therein to inform the masterbase station accordingly, and it can then send the thus-prepared firstpower headroom report to the master base station. Alternatively, it canprepare a secondary virtual power headroom report for the secondaryradio link between the mobile station and the secondary base station, itcan set a pre-determined flag therein to inform the master base stationaccordingly, and it can then send the thus-prepared secondary virtualpower headroom report to the master base station. According to stillanother alternative, the mobile station can prepare a secondary virtualpower headroom report for the secondary radio link, but with apre-determined power headroom value (e.g. a negative value) which isidentified by the master base station to mean that the secondary radiolink is becoming inactive for the uplink; the thus-prepared secondaryvirtual power headroom report is then sent from the mobile station tothe master base station.

Conversely, when the mobile station determines that the first radio linkbetween the mobile station and the master base station will becomeinactive for the uplink, it can prepare a secondary power headroomreport for the secondary radio link, it can set a pre-determined flagtherein to inform the secondary base station accordingly, and it canthen send the thus-prepared secondary power headroom report to thesecondary base station. Alternatively, the mobile station can prepare asecondary virtual power headroom report for the secondary radio link, itcan set a pre-determined flag therein to inform the secondary basestation accordingly, and it can then send the thus-prepared secondaryvirtual power headroom report to the secondary base station. Accordingto still another alternative, the mobile station can prepare a secondaryvirtual power headroom report for the secondary radio link, but with apre-determined power headroom value (e.g. a negative value) which isthen identified by the secondary base station to mean that the firstradio link is becoming inactive for the uplink; the thus-preparedsecondary virtual power headroom report is then sent from the mobilestation to the secondary base station.

According to a further improvement of the above reporting of thefirst/secondary radio link becoming inactive, the mobile station candetermine/estimate a length in time that the first/secondary radio linkis expected to be inactive for the uplink, and only in case thedetermined length in time exceeds a pre-determined length in time (e.g.100 or 200 ms etc), the corresponding base station (secondary/master)will be informed on the situation. This is advantageous such that thismechanism of reconfiguring the power distribution to be effective, andnot to be performed for very short times of inactivity.

Still another improvement of the above second aspect is that the basestation (first or secondary as appropriate) will return the powerdistribution to the previous state (i.e. to the power distribution ratiobefore the update) after a particular time, without having to be againinstructed by the mobile station. In more detail, as explained above,the master/secondary base stations are informed by the mobile stationwhen the secondary/first radio links become inactive, in order for themaster/secondary base station to update the power distribution andprovide the mobile station with updated values of the maximum outputpower to be used for uplink transmissions to the master/secondary basestation. In order to avoid the need for the mobile station to againinform the master/base station when the secondary/first radio linkbecomes active again, it is possible to configure a power control timerthat, when it expires, triggers the master/secondary base station toreturn to the power distribution ratio before the update. The value ofthe power control timer can either be pre-determined and configuredpreviously; or according to a further improvement, it may be informed bythe mobile station (which presumably has the best knowledge on when theinactive time of a radio link is expected to end) for each case e.g. bydirectly transmitting the corresponding power control timer value to themaster/secondary base station, or preferably by encoding the powercontrol timer value in the (e.g. negative) power headroom value of thesecondary virtual power headroom report transmitted from the mobilestation to the master/secondary base station to inform themaster/secondary base station on the secondary/first radio link becominginactive before (see above).

The above-mentioned power control timer is preferably started by themaster/secondary base station when determining and transmitting theupdated maximum output power of the mobile station for uplinktransmissions to the master/secondary base station, and runs for aparticular time (see above).

In a similar manner, the above-noted situation where the mobile stationdetermines that the first/secondary radio link enters a radio linkfailure state (i.e. becomes broken) is explained in the following.

When the mobile station determines that the secondary radio link fromthe mobile station to the secondary base station enters a radio linkfailure state, the mobile station shall inform the master base stationaccordingly over the working radio link. This may be done e.g. accordingto one of the following ways.

When the mobile station determines the radio link failure of thesecondary radio link to the secondary base station, it prepares a firstpower headroom report for the first radio link between the mobilestation and the master base station, it sets a correspondingpre-determined flag therein to inform the master base stationaccordingly, and it can then send the thus-prepared first power headroomreport for the first radio link to the master base station.Alternatively, the mobile station can prepare a secondary virtual powerheadroom report for the secondary radio link between the mobile stationand the secondary base station, it can set a corresponding predeterminedflag therein to inform the master base station accordingly, and it canthen send the thus-prepared secondary virtual power headroom report tothe master base station. According to still another alternative, themobile station can prepare a secondary virtual power headroom report forthe secondary radio link between the mobile station and the secondarybase station, but with a pre-determined virtual power headroom valuewhich is identified by the master base station to indicate the radiolink failure of the secondary radio link; the thus-prepared secondaryvirtual power headroom report is then sent from the mobile station tothe master base station.

After the master base station receives the information about thesecondary radio link failure, the master base station can determine anupdated value for the maximum output power of the mobile station foruplink transmissions to the master base station (P_(EMAX,MeNB)); thisupdated parameter is then transmit to the mobile station. For instance,the master base station can determine that the mobile station can useall of its maximum output power for uplink transmissions to the masterbase station, since no uplink transmissions to the secondary basestation are possible due to the secondary radio link failure. Accordingto a preferable solution, the master base station also initiates anappropriate procedure to solve the radio link failure of the secondaryradio link.

Conversely, when the mobile station determines the radio link failure ofthe first radio link to the master base station, it prepares a secondarypower headroom report for the secondary radio link, it sets acorresponding pre-determined flag therein to inform the secondary basestation accordingly, and it then sends the thus-prepared secondary powerheadroom report to the secondary base station. Alternatively, the mobilestation prepares a secondary virtual power headroom report for thesecondary radio link, it sets a corresponding pre-determined flagtherein to inform the secondary base station accordingly, and it thensends the thus-prepared secondary virtual power headroom report to thesecondary base station. According to still another alternative, themobile station prepares a secondary virtual power headroom report forthe secondary radio link, but with a pre-determined virtual powerheadroom value which is identified by the master base station toindicate the radio link failure of the first radio link; thethus-prepared secondary virtual power headroom report is then sent fromthe mobile station to the secondary base station.

After the secondary base station receives the information about thefirst radio link failure, the secondary base station can determine anupdated value for the maximum output power of the mobile station foruplink transmissions to the secondary base station (P_(EMAX,SeNB)); thisupdated parameter is then transmit to the mobile station. For instance,the secondary base station can determine that the mobile station can useall of its maximum output power for uplink transmissions to thesecondary base station, since no uplink transmissions to the master basestation are possible due to the first radio link failure. According to apreferable solution, the secondary base station also initiates anappropriate procedure to solve the radio link failure of the first radiolink.

An embodiment of the present disclosure provides a method for powerheadroom reporting in a mobile communication system. A mobile station isconnected via a first radio link to a master base station and at leastto one secondary base station via a secondary radio link. The mobilestation calculates a first power headroom report for the first radiolink between the mobile station and the master base station. The mobilestation transmits the calculated first power headroom report togetherwith information allowing the master base station to determineinformation on the pathloss of the secondary radio link between themobile station and the secondary base station, to the master basestation. Furthermore, the mobile station the mobile station calculates asecondary power headroom report for the secondary radio link between themobile station and the secondary base station, and transmitting thecalculated secondary power headroom report from the mobile station tothe secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the information, from which the master base station determines theinformation on the pathloss, is transmitted in form of a secondaryvirtual power headroom report for the secondary radio link between themobile station and the secondary base station. In said case, the mobilestation further calculates the secondary virtual power headroom reportfor the secondary radio link between the mobile station and thesecondary base station, based on a pre-configured virtual uplinkresource assignment for said secondary radio link to the secondary basestation. According to an advantageous variant of the embodiment of thepresent disclosure which can be used in addition or alternatively to theabove, the master base station determines an initial distribution of theavailable maximum transmit power of the mobile station between themaster base station and the secondary base station; which comprises thestep of determining a maximum output power of the mobile station foruplink transmissions to the master base station (P_(EMAX,MeNB)) and amaximum output power of the mobile station for uplink transmissions tothe secondary base station (P_(EMAX,SeNB)). The determined maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)), is transmitted from the masterbase station to the secondary base station, preferably in a signalingmessage transmitted on the interface between the master and secondarybase station. Then, either the determined maximum output power of themobile station for uplink transmissions to the master base station(P_(EMAX,MeNB)) and the determined maximum output power of the mobilestation for uplink transmissions to the secondary base station(P_(EMAX,SeNB)), are transmitted from the master base station to themobile station, preferably in a Radio Resource Control, RRC, message orin a Media Access Control, MAC, control element, OR the determinedmaximum output power of the mobile station for uplink transmissions tothe master base station (P_(EMAX,MeNB)), is transmitted from the masterbase station to the mobile station, preferably in a Radio ResourceControl, RRC, message or in a Media Access Control, MAC, controlelement, and the determined maximum output power of the mobile stationfor uplink transmissions to the secondary base station (P_(EMAX,SeNB)),is transmitted from the secondary base station to the mobile station.

According to an alternative and advantageous variant of the embodimentof the present disclosure which can be used in addition or alternativelyto the above, the master base station determines an initial distributionof the available maximum transmit power of the mobile station betweenthe master base station and the secondary base station, which comprisesthe step of determining a maximum output power of the mobile station foruplink transmissions to the master base station (P_(EMAX,MeNB)) and amaximum output power of the mobile station for uplink transmissions tothe secondary base station (P_(EMAX,SeNB)). Then, the determined maximumoutput power of the mobile station for uplink transmissions to themaster base station (P_(EMAX,MeNB)), and the determined maximum outputpower of the mobile station for uplink transmissions to the secondarybase station (P_(EMAX,SeNB)), are transmitted from the master basestation to the mobile station, preferably in a Radio Resource Control,RRC, message or in a Media Access Control, MAC, control element. Inaddition, the mobile station transmits to the secondary base station,information on the received maximum output power of the mobile stationfor uplink transmissions to the secondary base station (P_(EMAX,SeNB)).

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the step of, transmitting by the mobile station to the secondary basestation, information on the received maximum output power of the mobilestation for uplink transmissions to the secondary base station(P_(EMAX,SeNB)), comprises the steps of: determining for a secondaryvirtual power headroom report a cell-specific maximum output power,configured by the mobile station for uplink transmissions from themobile station to the secondary base station (P_(CMAX,SeNB)) based onthe received maximum output power of the mobile station for uplinktransmissions to the secondary base station (P_(EMAX,SeNB)), andtransmitting the determined cell-specific maximum output power,configured by the mobile station for uplink transmissions from themobile station to the secondary base station (P_(CMAX,SeNB)), from themobile station to the secondary base station, for the secondary basestation to determine the maximum output power of the mobile station foruplink transmissions to the secondary base station (P_(EMAX,SeNB)).

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the step of, transmitting by the mobile station to the secondary basestation, information on the received maximum output power of the mobilestation for uplink transmissions to the secondary base station(P_(EMAX,SeNB)), comprises the steps of: calculating by the mobilestation a secondary virtual power headroom report for the secondaryradio link between the mobile station and the secondary base station,based on a pre-configured virtual uplink resource assignment for saidsecondary radio link to the secondary base station, comprising thedetermination of a cell-specific maximum output power, configured by themobile station for uplink transmissions from the mobile station to thesecondary base station (P_(CMAX,SeNB)) based on the received maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)), and transmitting the calculatedsecondary virtual power headroom report and the determined cell-specificmaximum output power, configured by the mobile station, for uplinktransmissions from the mobile station to the secondary base station(P_(CMAX,SeNB)), from the mobile station to the secondary base station,for the secondary base station to determine the maximum output power ofthe mobile station for uplink transmissions to the secondary basestation (P_(EMAX,SeNB)).

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the master base station determines an updated distribution of theavailable maximum transmit power of the mobile station between themaster base station and the secondary base station, based on thedetermined information on the pathloss of the secondary radio linkbetween the mobile station and the secondary base station; thiscomprises determining updated values for the maximum output power of themobile station for uplink transmissions to the master base station(P_(EMAX,MeNB)) and the maximum output power of the mobile station foruplink transmissions to the secondary base station (P_(EMAX,SeNB)) Theupdated maximum output power of the mobile station for uplinktransmissions to the secondary base station (P_(EMAX,SeNB)), istransmitted from the master base station to the secondary base station.Then, either the updated maximum output power of the mobile station foruplink transmissions to the master base station (P_(EMAX,MeNB)) and theupdated maximum output power of the mobile station for uplinktransmissions to the secondary base station (P_(EMAX,SeNB)), aretransmitted from the master base station to the mobile station, OR theupdated maximum output power of the mobile station for uplinktransmissions to the master base station (P_(EMAX,MeNB)), is transmittedfrom the master base station to the mobile station, and the updatedmaximum output power of the mobile station for uplink transmissions tothe secondary base station (P_(EMAX,SeNB)), is transmitted from thesecondary base station to the mobile station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the calculated first power headroom report for the first radio link isan extended power headroom report that further comprises a cell-specificmaximum output power, configured by the mobile station for uplinktransmissions from the mobile station to the master base station(P_(CMAX,MeNB)), and the calculated secondary power headroom report forthe secondary radio link is an extended power headroom report thatfurther comprises a cell-specific maximum output power, configured bythe mobile station for uplink transmission from the mobile station tothe secondary base station (P_(CMAX,SeNB)).

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,when the mobile station determines that the secondary radio link betweenthe mobile station and the secondary base station will become inactivefor the uplink, the mobile station provides information to the masterbase station about the secondary radio link becoming inactive for theuplink. In a preferable solution, the information, about the secondaryradio link becoming inactive for the uplink, is provided to the masterbase station in the form of:

-   -   a bit flag with a pre-determined value in the first power        headroom report for the first radio link between the mobile        station and the master base station, or    -   a bit flag with a pre-determined value in the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, or    -   a pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the mobile station determines a length in time that the secondary radiolink is expected to be inactive for the uplink, and only in case thedetermined length in time exceeds a pre-determined length in time, themobile station provides information to the master base station about thesecondary radio link becoming inactive for the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the information, about the secondary radio link becoming inactive forthe uplink, is provided to the master base station in the form of apre-determined power headroom value of the secondary virtual powerheadroom report for the secondary radio link between the mobile stationand the secondary base station. The pre-determined power headroom valueis a pre-determined negative value, preferably encoding time informationabout a length in time that the secondary radio link is expected by themobile station to be inactive for the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the master base station determines an updated distribution of theavailable maximum transmit power of the mobile station between themaster base station and the secondary base station, based on thereceived information about the secondary radio link becoming inactivefor the uplink, comprising at least determining an updated value for themaximum output power of the mobile station for uplink transmissions tothe master base station (P_(EMAX,MeNB)) The master base stationtransmits, the updated maximum output power of the mobile station foruplink transmissions to the master base station (P_(EMAX,MeNB)), to themobile station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the master base station starts a power control timer, when determiningand transmitting the updated maximum output power of the mobile stationfor uplink transmissions to the master base station (P_(EMAX,MeNB)) Uponexpiry of the power control timer, the master base station transmits,the maximum output power of the mobile station for uplink transmissionsto the master base station (P_(EMAX,MeNB)) before the update, to themobile station. The power control timer is preferably configured:

-   -   with a pre-determined time value, or    -   a time value as indicated by the mobile station in the received        secondary virtual power headroom report with the pre-determined        negative power headroom value, in case the information about the        secondary radio link becoming inactive for the uplink is        provided to the master base station in the form of a        pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, and wherein the        predetermined power headroom value is a pre-determined negative        value, preferably encoding time information about a length in        time that the secondary radio link is expected to be inactive        for the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,when the mobile station determines that the first radio link between themobile station and the master base station will become inactive for theuplink, the mobile station provides information to the secondary basestation about the first radio link becoming inactive for the uplink. Theinformation, about the first radio link becoming inactive for theuplink, is provided to the secondary base station in the form of:

-   -   a bit flag with a pre-determined value in the secondary power        headroom report for the secondary radio link between the mobile        station and the secondary base station, or    -   a bit flag with a pre-determined value in the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, or    -   a pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the mobile station determines a length in time that the first radio linkis expected to be inactive for the uplink, and wherein only in case thedetermined length in time exceeds a predetermined length in time, themobile station provides information to the secondary base station aboutthe first radio link becoming inactive for the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the information, about the first radio link becoming inactive for theuplink, is provided to the secondary base station in the form of apre-determined power headroom value of the secondary virtual powerheadroom report for the secondary radio link between the mobile stationand the secondary base station. In said case, the pre-determined powerheadroom value is a pre-determined negative value, preferably encodingtime information about a length in time that the first radio link isexpected by the mobile station to be inactive for the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the secondary base station determines an updated value for the maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)) The secondary base stationtransmits, the updated maximum output power of the mobile station foruplink transmissions to the secondary base station (P_(EMAX,SeNB)), tothe mobile station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the secondary base station starts a power control timer, whendetermining and transmitting the updated maximum output power of themobile station for uplink transmissions to the secondary base station(P_(EMAX,SeNB)). Upon expiry of the power control timer, the master basestation transmits, the maximum output power of the mobile station foruplink transmissions to the master base station (P_(EMAX,SeNB)) beforethe update, to the mobile station. Preferably, the power control timeris configured:

-   -   with a pre-determined time value, or    -   a time value as indicated by the mobile station in the received        secondary virtual power headroom report with the pre-determined        negative power headroom value, in case the information about the        first radio link becoming inactive for the uplink is provided to        the secondary base station in the form of a pre-determined power        headroom value of the secondary virtual power headroom report        for the secondary radio link between the mobile station and the        secondary base station, and wherein the pre-determined power        headroom value is a pre-determined negative value, preferably        encoding time information about a length in time that the first        radio link is expected by the mobile station to be inactive for        the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,when the secondary radio link from the mobile station to the secondarybase station enters a radio link failure state, the mobile stationprovides information to the master base station about the radio linkfailure of the secondary radio link preferably in the form of:

-   -   a bit flag with a pre-determined value in the first power        headroom report for the first radio link between the mobile        station and the master base station, or    -   a bit flag with a pre-determined value in the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, or    -   a pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the master base station determines an updated distribution of theavailable maximum transmit power of the mobile station between themaster base station and the secondary base station, based on thereceived information about the radio link failure of the secondary radiolink; which comprises at least the step of determining an updated valuefor the maximum output power of the mobile station for uplinktransmissions to the master base station (P_(EMAX,MeNB)). The masterbase station transmits, the updated value for the maximum output powerof the mobile station for uplink transmissions to the master basestation (P_(EMAX,MeNB)), to the mobile station. Preferably, the masterbase station initiates an appropriate procedure to solve the radio linkfailure of the secondary radio link.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,when the first radio link from the mobile station to the secondary basestation enters a radio link failure state, the mobile station providesinformation to the secondary base station about the radio link failureof the first radio link preferably in the form of:

-   -   a bit flag with a pre-determined value in the secondary power        headroom report for the secondary radio link between the mobile        station and the secondary base station, or    -   a bit flag with a pre-determined value in the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, or    -   a pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the secondary base station determines an updated value for the maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)) The secondary base stationtransmits, the updated maximum output power of the mobile station foruplink transmissions to the secondary base station (P_(EMAX,SeNB)), tothe mobile station. Preferably, the secondary base station initiates anappropriate procedure to solve the radio link failure of the first radiolink.

The first embodiment of the present disclosure further provides a mobilestation for power headroom reporting in a mobile communication system,wherein the mobile station is connectable via a first radio link to amaster base station and at least to one secondary base station via asecondary radio link A processor of the mobile station calculates afirst power headroom report for the first radio link between the mobilestation and the master base station. A transmitter of the mobile stationtransmits the calculated first power headroom report together withinformation allowing the master base station to determine information onthe pathloss of the secondary radio link between the mobile station andthe secondary base station, to the master base station. The processorfurther calculates a secondary power headroom report for the secondaryradio link between the mobile station and the secondary base station.The transmitter then transmits the calculated secondary power headroomreport to the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the information, from which the master base station determines theinformation on the pathloss, is transmitted in form of a secondaryvirtual power headroom report for the secondary radio link between themobile station and the secondary base station. In said case, theprocessor calculates the secondary virtual power headroom report for thesecondary radio link between the mobile station and the secondary basestation, based on a pre-configured virtual uplink resource assignmentfor said secondary radio link to the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,a receiver of the mobile station receives a maximum output power of themobile station for uplink transmissions to the secondary base station(P_(EMAX,SeNB)) and/or receives a maximum output power of the mobilestation for uplink transmissions to the master base station(P_(EMAX,MeNB)) from the master base station, preferably in a RadioResource Control, RRC, message or in a Media Access Control, MAC,control element.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,a receiver of the mobile station receives a maximum output power of themobile station for uplink transmissions to the secondary base station(P_(EMAX,SeNB)), wherein the transmitter transmits to the secondary basestation, information on the received maximum output power of the mobilestation for uplink transmissions to the secondary base station(P_(EMAX,SeNB)).

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the processor determines for a secondary virtual power headroom report acell-specific maximum output power, configured by the mobile station foruplink transmissions from the mobile station to the secondary basestation (P_(CMAX,SeNB)) based on the received maximum output power ofthe mobile station for uplink transmissions to the secondary basestation (P_(EMAX,SeNB)). The transmitter transmits the determinedcell-specific maximum output power, configured by the mobile station foruplink transmissions from the mobile station to the secondary basestation (P_(CMAX,SeNB)), to the secondary base station, for thesecondary base station to determine the maximum output power of themobile station for uplink transmissions to the secondary base station(P_(EMAX,SeNB)).

According to an alternative advantageous variant of the embodiment ofthe present disclosure which can be used in addition or alternatively tothe above, the processor calculates a secondary virtual power headroomreport for the secondary radio link between the mobile station and thesecondary base station, based on a pre-configured virtual uplinkresource assignment for said secondary radio link to the secondary basestation, comprising the determination of a cell-specific maximum outputpower, configured by the mobile station for uplink transmissions fromthe mobile station to the secondary base station (P_(CMAX,SeNB)) basedon the received maximum output power of the mobile station for uplinktransmissions to the secondary base station (P_(EMAX,SeNB)). Thetransmitter transmits the calculated secondary virtual power headroomreport and the determined cell-specific maximum output power, configuredby the mobile station, for uplink transmissions from the mobile stationto the secondary base station (P_(CMAX,SeNB)), to the secondary basestation, for the secondary base station to determine the maximum outputpower of the mobile station for uplink transmissions to the secondarybase station (P_(EMAX,SeNB)).

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,when the processor determines that the secondary radio link between themobile station and the secondary base station will become inactive forthe uplink, the transmitter provides information to the master basestation about the secondary radio link becoming inactive for the uplink,preferably in the form of:

-   -   a bit flag with a pre-determined value in the first power        headroom report for the first radio link between the mobile        station and the master base station, or    -   a bit flag with a pre-determined value in the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, or    -   a pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the processor determines a length in time that the secondary radio linkis expected to be inactive for the uplink, and wherein only in case thedetermined length in time exceeds a pre-determined length in time, thetransmitter provides information to the master base station about thesecondary radio link becoming inactive for the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the information, about the secondary radio link becoming inactive forthe uplink, is provided to the master base station in the form of apre-determined power headroom value of the secondary virtual powerheadroom report for the secondary radio link between the mobile stationand the secondary base station. In said case, the processor sets thepre-determined power headroom value to a pre-determined negative value,preferably encoding time information about a length in time that thesecondary radio link is expected by the mobile station to be inactivefor the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,when the processor determines that the first radio link between themobile station and the master base station will become inactive for theuplink, the transmitter provides information to the secondary basestation about the first radio link becoming inactive for the uplink,preferably in the form of:

-   -   a bit flag with a pre-determined value in the secondary power        headroom report for the secondary radio link between the mobile        station and the secondary base station, or    -   a bit flag with a pre-determined value in the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, or    -   a pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the processor determines a length in time that the first radio link isexpected to be inactive for the uplink, and wherein only in case thedetermined length in time exceeds a pre-determined length in time, thetransmitter provides information to the secondary base station about thefirst radio link becoming inactive for the uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the information, about the first radio link becoming inactive for theuplink, is provided to the secondary base station in the form of apre-determined power headroom value of the secondary virtual powerheadroom report for the secondary radio link between the mobile stationand the secondary base station. In said case, the processor sets thepre-determined power headroom value to a pre-determined negative value,preferably encoding time information about a length in time that thefirst radio link is expected by the mobile station to be inactive forthe uplink.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,when the processor determines that the secondary radio link between themobile station and the secondary base station enters a radio linkfailure, the transmitter provides information to the master base stationabout the first radio link failure preferably in the form of:

-   -   a bit flag with a pre-determined value in the first power        headroom report for the first radio link between the mobile        station and the master base station, or    -   a bit flag with a pre-determined value in the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, or    -   a pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,when the processor determines that the first radio link between themobile station and the master base station enters a radio link failure,the transmitter provides information to the secondary base station aboutthe secondary radio link failure preferably in the form of:

-   -   a bit flag with a pre-determined value in the secondary power        headroom report for the secondary radio link between the mobile        station and the secondary base station, or    -   a bit flag with a pre-determined value in the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station, or    -   a pre-determined power headroom value of the secondary virtual        power headroom report for the secondary radio link between the        mobile station and the secondary base station.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,a receiver receives an updated value for the maximum output power of themobile station for uplink transmissions to the secondary base station(P_(EMAX,SeNB)), and receives an updated value for the maximum outputpower of the mobile station for uplink transmissions to the master basestation (P_(EMAX,MeNB)).

The first embodiment of the present disclosure further provides a masterbase station for receiving power headroom reports from a mobile stationin a mobile communication system. The mobile station is connected via afirst radio link to the master base station and at least to onesecondary base station via a secondary radio link A receiver of themaster base station receives from the mobile station a first powerheadroom report together with information allowing the master basestation to determine information on the pathloss of the secondary radiolink between the mobile station and the secondary base station. Aprocessor of the master base station determines information on thepathloss of the secondary radio link between the mobile station and thesecondary base station, based on the received information.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the processor determines an initial distribution of the availablemaximum transmit power of the mobile station between the master basestation and the secondary base station; which comprises the step ofdetermining a maximum output power of the mobile station for uplinktransmissions to the master base station (P_(EMAX,MeNB)) and a maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)). A transmitter of the master basestation transmits the determined maximum output power of the mobilestation for uplink transmissions to the secondary base station(P_(EMAX,SeNB)), to the secondary base station, preferably in asignaling message transmitted on the interface between the master andsecondary base station. The transmitter transmits the determined maximumoutput power of the mobile station for uplink transmissions to themaster base station (P_(EMAX,MeNB)) and/or the determined maximum outputpower of the mobile station for uplink transmissions to the secondarybase station (P_(EMAX,SeNB)), to the mobile station, preferably in aRadio Resource Control, RRC, message or in a Media Access Control, MAC,control element.

According to an advantageous variant of the embodiment of the presentdisclosure which can be used in addition or alternatively to the above,the processor determines an updated distribution of the availablemaximum transmit power of the mobile station between the master basestation and the secondary base station, based on the determinedinformation on the pathloss of the secondary radio link between themobile station and the secondary base station; which comprises the stepof determining updated values for the maximum output power of the mobilestation for uplink transmissions to the master base station(P_(EMAX,MeNB)) and the maximum output power of the mobile station foruplink transmissions to the secondary base station (P_(EMAX,SeNB)). Atransmitter of the master base station transmits the updated maximumoutput power of the mobile station for uplink transmissions to thesecondary base station (P_(EMAX,SeNB)), to the secondary base station.The transmitter transmits the updated maximum output power of the mobilestation for uplink transmissions to the master base station(P_(EMAX,MeNB)) and/or the updated maximum output power of the mobilestation for uplink transmissions to the secondary base station(P_(EMAX,SeNB)), to the mobile station.

A “mobile station” or “mobile node” is a physical entity within acommunication network. One node may have several functional entities. Afunctional entity refers to a software or hardware module thatimplements and/or offers a predetermined set of functions to otherfunctional entities of a node or the network. Nodes may have one or moreinterfaces that attach the node to a communication facility or mediumover which nodes can communicate. Similarly, a network entity may have alogical interface attaching the functional entity to a communicationfacility or medium over it may communicate with other functionalentities or correspondent nodes.

The term “master base station” used in the claims and throughout thedescription of the present disclosure is to be construed as used in thefield of dual connectivity of 3GPP LTE-A; thus, other terms are macrobase station, or master/macro eNB; or serving base station or any otherterminology to be decided later by 3GPP. Similarly, the term “secondarybase station” used in the claims and throughout the description is to beconstrued as used in the field of dual connectivity of 3GPP LTE-A; thus,other terms are slave base station, or secondary/slave eNB or any otherterminology to be decided later by 3GPP.

The term “radio link” used in the claims and throughout the descriptionof the present disclosure is to be understood in a broad way as theradio connection between the mobile station and a base station.

The term “power headroom report” shall refer, for a particularembodiment of the present disclosure, to the power headroom report asdefined in 3GPP, preferably shall refer to the extended power headroomreport as defined in 3GPP.

The term “virtual power headroom report” shall refer, for a particularembodiment of the present disclosure, to the virtual power headroomreport as defined in 3GPP.

In the following, several embodiments of the present disclosure will beexplained in detail. For exemplary purposes only, most of theembodiments are outlined in relation to a radio access scheme accordingto 3GPP LTE (Release 8/9) and LTE-A (Release 10/11) mobile communicationsystems, partly discussed in the Technical Background section above. Itshould be noted that the present disclosure may be advantageously usedfor example in a mobile communication system such as 3GPP LTE-A (Release12) communication systems as described in the Technical Backgroundsection above. These embodiments are described as implementations foruse in connection with and/or for enhancement of functionality specifiedin 3GPP LTE and/or LTE-A. In this respect, the terminology of 3GPP LTEand/or LTE-A is employed throughout the description. Further, exemplaryconfigurations are explored to detail the full breadth of the presentdisclosure.

The explanations should not be understood as limiting the presentdisclosure, but as a mere example of the embodiments to betterunderstand the present disclosure. A skilled person should be aware thatthe general principles of the present disclosure as laid out in theclaims can be applied to different scenarios and in ways that are notexplicitly described herein. Correspondingly, the following scenariosassumed for explanatory purposes of the various embodiments shall notlimit the present disclosure as such.

In connection with the present disclosure, various implementations willbe explained. To simplify the illustration of the principles of thepresent disclosure, several assumptions are made; however, it should benoted that these assumptions should not be interpreted as limiting thescope of the present disclosure, as broadly defined by the claims.

The present disclosure will be described with reference to FIGS. 17 to23. A dual connectivity scenario in a small cell environment is assumed,where the UE is connected to both a MeNB and a SeNB respectively via afirst and secondary radio link. It should be noted however that thepresent disclosure is not restricted to this scenario; for instance,scenarios where the UE is connected to a MeNB and at least two SeNBs arealso possible.

According to the present disclosure, one of the MeNB and SeNB has theresponsibility to control the power distribution for the UE for uplinktransmissions to the MeNB and uplink transmissions to the SeNB. For theensuing description of the present disclosure, it is assumed that theMeNB takes the responsibility to control the power distribution;however, the principles of the present disclosure can be equally applied(with the obviously necessary changes) to a scenario where the SeNB ischosen to take the responsibility to control the power distribution.

In accordance with power control as already defined by 3GPP (pleaserefer to background section), a UE is usually determining its maximumoutput power that it is allowed to use for its uplink transmissionsbased on its powerclass and a maximum power limit configured andsignaled by the eNB, i.e P_(EMAX). P_(EMAX) is determined by the (M)eNB,and the UE is provided with same; the UE in turn possibly appliesfurther power restrictions such as MPR, A-MPR to lower its maximumtransmission power in order to be able to meet the requirements onsignal quality, spectrum emission mask and spurious emissions.

When a UE, which is connected to an MeNB, enters dual connectivitystate, i.e. when a cell controlled by a SeNB is configured and added, itis advantageous according to the present disclosure to determine aninitial power distribution of the available output power of a UE foruplink transmissions among the MeNB and SeNB, i.e. determine twoparameters P_(EMAX,MeNB) and P_(EMAX,SeNB). P_(EMAX,MeNB) shall beunderstood as the maximum output power that the mobile station shall usefor uplink transmissions to the MeNB; correspondingly, P_(EMAX,SeNB)shall be understood as the maximum output power that the mobile stationshall use for uplink transmissions to the SeNB. On a more general level,the MeNB may determine the maximum power the mobile station is permittedto transmit in each UL component carrier or cell or set of configured ULcomponent carrier that belong to the same or different eNB. For the casethat one eNB—may it MeNB and SeNB—has more component carrier under itscontrol, the corresponding NodeB could further distribute the signaledmaximum allowed uplink transmission power (P_(EMAX,MeNB) andP_(EMAX,SeNB)) among the component carriers.

In order to determine an efficient and reasonable initial powerdistribution ratio, i.e. the two parameters P_(EMAX,MeNB) andP_(EMAX,SeNB), the MeNB can take into account one or various of thefollowing parameters:

-   -   the pathloss on the two radio links between the UE and the        MeNB/SeNB, which gives an indication of how far the UE is away        from the MeNB respectively SeNB (UE-distance to MeNB and SeNB)        and thus allowing conclusions on how much power might be        necessary by the UE for data transmissions to the MeNB and SeNB        and the possible power distribution ratio which is best    -   information on the traffic load handled by MeNB and SeNB    -   uplink resource availability for the two radio links

As a result, the MeNB determines how the maximum allowed uplinktransmission power is distributed between the UE for uplinktransmissions to MeNB and SeNB, i.e. the MeNB determines the values ofP_(EMAX,MeNB) and P_(EMAX,SeNB) For example, for a mobile terminal witha maximum transmission power of 23 dBm, communicating with an MeNB andSeNB, the maximum allowed uplink transmission powers may be set to 20dBm for each eNB. Another example would be to set the power distributionratio to 1 to 2, where P_(EMAX,MeNB)=P_(CMAX)/3 andP_(CMAX,SeNB)=2*P_(CMAX)/3. It should be generally understood thatP_(CMAX) refers to the maximum uplink transmission power available bythe UE. As MeNB doesn't exactly know the P_(CMAX) set by the mobilestation, MeNB would need to either do some prediction of the value orassume always the worst case situation where the mobile station appliesthe largest power reduction allowed by the specification, i.e. MPR,which would be equal to assume P_(CMAX) _(_) _(L) as P_(CMAX).

After the determination of the initial values of P_(EMAX,MeNB) andP_(EMAX,SeNB) by the MeNB, these parameters are to be distributed to theSeNB and UE for use in the respective power control procedures. Inparticular, the UE needs both P_(EMAX,MeNB) and P_(EMAX,SeNB) toproperly control the output power for uplink transmissions to both basestations, MeNB and SeNB. The SeNB however only needs the parameterP_(EMAX,SeNB).

FIGS. 17-19 illustrate different implementations as to how exactly thetwo parameters P_(EMAX,MeNB) and P_(EMAX,SeNB) can be distributed fromthe MeNB, so as to be received by the SeNB and the UE. According to thefirst alternative as illustrated by FIG. 17, the MeNB can transmitP_(EMAX,MeNB) and P_(EMAX,SeNB) to the UE, and P_(EMAX,SeNB) to theSeNB. Furthermore, in this particular scenario of FIG. 17, theparameters P_(EMAX,MeNB) and P EMAX,SeNB are transmitted via RRCsignaling, i.e. as an RRC configuration. Alternatively, but not shown inFIG. 17, the two parameters P_(EMAX,MeNB) and P_(EMAX,SeNB) can also betransmitted from the MeNB to the UE as a MAC control element.Furthermore, the parameter P_(EMAX,SeNB) is preferably transmitted fromthe MeNB to the SeNB over the Xn interface.

According to another alternative implementation, as depicted in FIG. 18,the parameter P_(EMAX,SeNB) is transmitted from the MeNB to the SeNB, inthe same manner as for FIG. 17; i.e. preferably over the Xn interface.However, it is the SeNB, not the MeNB, which transmits the parameterP_(EMAX,SeNB) to the UE; this may be done by use of a MAC controlelement as depicted in FIG. 18. The MeNB transmits the parameter PEMAX,MeNB to the UE, e.g. as part of a RRC configuration oralternatively (not shown in FIG. 18) in a MAC control element.

According to still another implementation, as depicted in FIG. 19, theMeNB transmits P_(EMAX,MeNB) and P_(EMAX,SeNB) to the UE. Then, contraryto the implementations of FIGS. 17 and 18, the MeNB does not need totransmit P_(EMAX,SeNB) to the SeNB, since this is done by the UE asfollows. The UE can transmit P_(EMAX,SeNB) to the SeNB in several ways.Not depicted in FIG. 19 is the simple way that the UE, after receivingthe P EMAX,SeNB from the MeNB, forwards this parameter directly furtherto the SeNB, e.g. within a particular MAC control element.Alternatively, the UE may calculate the power related parameter, virtualP_(CMAX,SeNB) (which is the maximum power used for the calculation ofthe virtual power headroom), based on the received P_(EMAX,SeNB).Basically, according to a virtual power headroom report, P_(CMAX,SeNB)is equal to P_(CMAX) _(_) _(H,c) which is equal to P_(EMAX,SeNB).Therefore, the UE can transmit the virtual P_(CMAX,SeNB) to the SeNB, asdepicted in FIG. 19. According to another implementation, the UE aftercalculating the virtual P_(CMAX,SeNB), as explained above, alsocalculates the virtual power headroom report for the secondary link(V-PHR_(SeNB)) and transmits both together to the SeNB. One way oftransmitting these two parameters V-PHR_(SeNB) and virtual P_(CMAX,SeNB)together to the SeNB is depicted in FIG. 20, which illustrates thestructure of a MAC control element for a power headroom report,including an extended power headroom report for the secondary radio linkto the SeNB (2^(nd) to 5^(th) line; see also corresponding part ofbackground section regarding extended PHR, Type 2 vs Type 1, withadditional P_(CMAX,c) etc.) and further includes the virtual powerheadroom value and the corresponding P_(CMAX,SeNB) which is usually nottransmitted with the virtual PHR.

As explained above exemplarily in relation to FIGS. 17 to 19, the SeNBand the UE are provided with the necessary parameters, P_(EMAX,MeNB) andP_(EMAX,SeNB), so as to apply same to the usual power control procedureas already standardized by 3GPP, which means that the UE proceeds tocalculate its P_(CMAX,SeNB) and P_(CMAX,MeNB) to be used for uplinktransmissions scheduled by the MeNB and the SeNB (possibly applyingfurther a power reduction as needed).

Accordingly, by one of the various alternatives it is possible todistribute the parameters P_(EMAX,SeNB) and P_(EMAX,MeNB) from the MeNBto the SeNB and UE. These same alternatives can also be used later inconnection with further improvements where updated values of theseparameters are to be distributed accordingly to the SeNB and/or the UE.

In the above, basically the initialization of the power distributionbetween MeNB and SeNB has been explained, where initial values for theparameters P_(EMAX,SeNB) and P_(EMAX,MeNB) are determined by the MeNB(responsible for the power distribution control) and then transmitted tothe SeNB and UE so as to apply them to the uplink schedulingrespectively uplink transmissions. In the following, the furtheroperation will be explained, according to which the initially-configuredpower distribution can be updated so as to maintain an efficient powerdistribution ratio between uplink transmissions from the UE to the MeNBand to the SeNB. Again, the MeNB is assumed to be responsible forupdating the power distribution as needed, i.e. to determine updatedvalues for the parameters P_(EMAX,SeNB) and P_(EMAX,MeNB) and todistribute same to the SeNB and/or the UE as needed (according to one ofthe various alternatives presented above).

To said end, the MeNB shall use e.g. information on the pathloss on atleast one of the two radio links, or information on the traffic load; inline with the determination of the initial power distribution. While theMeNB may already have some of the information, such as the traffic loadfor both radio links (e.g. in cases where the MeNB forwards the SeNBdata to the SeNB), the MeNB is to be provided with other informationwhich he would normally not have access to.

In particular, the MeNB can determine the information on the pathloss ofthe first radio link between the UE and the MeNB, from (extended) powerheadroom reports received from the UE for the first radio link. As canbe seen from the equations for the power headroom value, as set out inthe background section and as defined by the current standardization,the information on the pathloss (PL) is one of various parameters thatare used by the UE to calculate the power headroom value provided to theMeNB, and the MeNB knowing most of the remaining parameters of theequation can derive information on the pathloss, as determined by theUE. In addition to the power headroom reports, the MeNB can use themobility measurement reports such as RSRP (Reference Signal ReceivedPower) and RSRQ (Reference Signal Received Quality) in order to retrievethe pathloss information for the first radio link.

On the other hand, the MeNB is not aware of the pathloss determined bythe UE for the secondary radio link between the UE and the SeNB, whichhowever is also important for the updating of the power distributionratio. The information on the pathloss can be provided in several waysto the MeNB.

Of course, the information on the pathloss can be provided directly fromthe UE to the MeNB, e.g. in a corresponding MAC control element or otherappropriate message.

Alternatively, the UE can calculate and prepare a virtual power headroomreport, including a virtual power headroom value, for the secondaryradio link to the SeNB. The definition of the V-PHR according to 3GPP(see background section for details) is such that the MeNB receiving thevalue of PH_(virtual), from the UE can derive the information on thepathloss therefrom. This is in contrast to the normal power headroomreport, which power headroom value is calculated by the UE based on aresource assignment unknown to the MeNB (i.e. M_(PUSCH)(i) which is thebandwidth of the PUSCH resource assignment expressed in number ofresource blocks valid for sub-frame i). For this reason, the MeNB cannot derive the pathloss information therefrom. As outlined in thetechnical background section, the virtual PH is according to 3GPPTS36.213 calculated asPH _(virtual,c)(i)=P _(CMAX,H,c) −{P ₀ _(_) _(PUSCH)(j)+a(j)+PL _(c)+f(i)}

The parameter f(i) represents the UE-specific TPC commands, which can beconfigured either in a accumulative or absolute fashion. Since the MeNBdoes not know the TPC commands sent by SeNB, in an further alternativeembodiment the f(i) could be set to zero for the calculation of thevirtual power headroom value for the secondary link.

The V-PHR for the secondary radio link can be provided to the MeNB,which in turn can derive the information on the pathloss therefrom. Forexample, the usual power headroom reporting could be adapted such thatthe UE transmits the V-PHR for the secondary radio link together withthe usual power headroom report to the MeNB. This is apparent from FIG.22, which illustrates the MAC control element for the PHR_(MeNB) andVirtual PHR_(SeNB).

This changes the usual power headroom reporting such that the UE notonly prepares power headroom reports for the first and secondary radiolinks and transmits them respectively to the MeNB and SeNB, as alreadydefined by the 3GPP standard (see e.g. FIG. 23 for the usual powerheadroom report). Additionally, the UE prepares a virtual power headroomreport for the secondary radio link, which is then transmitted by the UEto the MeNB (not to the SeNB) (preferably together with the usual powerheadroom report for the first radio link).

One exemplary UE behavior according to this additional embodiment isshown in FIG. 21 where the UE, more in particular the MAC entity whichis handling MAC functionalities/protocol towards the MeNB MAC_(MeNB),generates a power headroom report which contains the extended PHRinformation for the group of cells associated with the MeNB (as alreadydefined by the 3GPP standard Rel-10) and virtual power headroominformation for the group of cells associated to the SeNB and transmitsthem to the MeNB. According to the exemplary implementation shown inFIG. 21 the UE, or more in particular the MAC_(SeNB), generates extendedpower headroom information for the group of cells associated to the SeNBand transmits them to the SeNB. As mentioned above already the inventionshould not be limited to cases where virtual power headroom informationof the other (secondary) radio link is only provided to the MeNB. Thesame principles could be also applied for the case where virtual powerheadroom information for the group of cells associated to the MeNB isprovided to the SeNB together with power headroom information for thegroup of cells associated to the SeNB.

As shown in FIG. 22 the virtual power headroom for the SeNB should bebasically a type 1 PH. However it would be also possible to include avirtual type 2 Power headroom, i.e. based a reference PUCCH format. Thevirtual PH would be according to FIG. 22 always appended at the end ofthe usual power headroom report for the MeNB link.

According to another embodiment the virtual power headroom informationis provided together with in identifier of the SeNB. This is inparticular necessary for deployments where UE is connected to one MeNBand more than one SeNB. The reserved bit “R” and the “V” could be forexample used to signal the identifier.

In a further alternative embodiment the virtual PHR info is transmittedin a separate power headroom MAC control element, which is identified bya predefined identifier, e.g. logical channel ID. The format of thissecondary power headroom report could be similar to power headroom MACcontrol element or extended power headroom MAC control element definedin TS36.321.

Correspondingly, in one specific implementation, the standard powerheadroom reporting could be changed such that every time a PHR for theMeNB is triggered (e.g. due to a periodic reporting or due to anevent-triggered reporting like a significant pathloss change), the UEshall always sent the normal PHR for the MeNB together with the virtualPHR for the SeNB to the MeNB.

In summary, the MeNB shall receive the necessary information allowing itto update the power distribution, preferably on a regular basis. Thisincludes the determination of updated values for the parametersP_(EMAX,SeNB) and P_(EMAX,MeNB) and the distribution of same to the SeNBand/or the UE as needed (e.g. according to one of the variousalternatives presented above and explained in connection with FIGS.17-19).

In the above, the update of the power distribution ratio has beenexplained for scenarios in which the power distribution ratio may changedue to e.g. movement of the UE where the pathloss changes and thus theupdate of the power distribution ratio is advantageous. However, thepower distribution ratio shall also be updated for other situations,such as when a particular radio link (e.g. the first or second radiolink) is not used in the uplink, or is not usable. In more detail, aradio link may become inactive in the uplink for several reasons. Forinstance, when the UE expects to not receive any downlink data(including any uplink resource assignments) for a particular length oftime, it may enter a DRX state so as to save battery (see alsocorresponding background chapter on DRX).

Another example is when there is a radio link failure for a radio link(at least for the uplink), i.e. a radio link fails, is not usable anymore for uplink transmissions, and thus enters a radio link failurestate. In at least the above two cases, no uplink transmissions aredone/possible for one of the two radio links, such that the powerdistribution ratio is not efficient, since the power assigned to uplinktransmissions over the unused/broken radio link is wasted, and shallbetter be used for uplink transmissions over the other remainingused/non-broken radio link A further improvement of the presentdisclosure to achieve this will be explained in the following.

First the case will be explained where the radio link becomes inactivefor the uplink. The UE is monitoring the uplink transmissions over thetwo radio links and thus is able to determine when the radio linkbecomes inactive for the uplink, i.e. when no uplink transmissions areexpected to be transmitted from the UE to the MeNB or SeNB. As alreadynoted above, this may be the case when the UE enters DRX mode.

In a more preferable solution, to avoid that lengths of inactivity, thatare too short, trigger the re-configuration of the power distributionratio, the UE may also determine the expected length of the inactivityfor the radio link, and may only proceed with the present disclosure (asexplained below), when the expected length of radio link inactivity foruplink exceeds a certain time threshold; e.g. the threshold can bepredetermined and configured by the MeNB via RRC.

In any case, the UE which is monitoring the possible inactivity of thetwo radio links for uplink transmission to MeNB/SeNB, will eventuallydetermine that one of the two radio links indeed becomes inactive.

Assuming that the UE determines that the first radio link to the MeNBbecomes inactive for the uplink (preferably for a length in time longerthan the pre-determined time threshold), then, the SeNB shall beinformed in said respect, i.e. about the first radio link becominginactive in the uplink. Similarly, when the UE determines that thesecondary radio link to the SeNB becomes inactive for the uplink(preferably for a length in time longer than the pre-determinedthreshold), then, the MeNB shall be informed in said respect, i.e. aboutthe secondary radio link becoming inactive in the uplink.

The UE may inform the SeNB/MeNB, about the inactivity of the respectiveradio link to the other eNB (i.e. MeNB/SeNB), in at least one of thefollowing ways.

The UE can use these situations as a trigger for power headroomreporting, and thus prepare a power headroom report in which acorresponding pre-determined flag is set to a pre-determined value (suchas “1”), which can be then understood by the receiving base station thatthe radio link becomes inactive for the uplink. In more detail, for thecase of the first radio link to the MeNB becoming inactive, the UEprepares a power headroom report for the secondary radio link to theSeNB, and sets a flag in said prepared secondary power headroom report(e.g. one of the reserved flags “R” or one of the V-flags in the PHR MACCE of FIG. 23). Alternatively, the UE prepares a virtual power headroomreport for the secondary radio link to the SeNB, and sets a flag in saidsecondary virtual power headroom report (e.g. one of the R-flags in thelast two lines of the PHR MAC CE as illustrates in FIG. 20). Accordingto still another alternative, the UE prepares a virtual power headroomreport for the secondary radio link to the SeNB and sets the virtualpower headroom value of the secondary virtual power headroom report to aparticular pre-determined value (e.g. to a negative value; a usual V-PHcannot be negative). In any case, the SeNB receives from the UE one ofthe above-noted indications (i.e. flags or pre-determined V-PH value)and can derive therefrom that the first radio link is inactive for theuplink.

Conversely, for the case where the secondary radio link to the SeNBbecomes inactive, the UE prepares a power headroom report for the firstradio link to the MeNB, and sets a flag in said prepared first powerheadroom report (e.g. one of the reserved flags “R” or one of theV-flags in the PHR MAC CE as depicted in the first 5 lines of FIG. 22).Alternatively, the UE prepares a virtual power headroom report for thesecondary radio link between the UE and the SeNB (which is also used forproviding the MeNB with information on the pathloss of the secondaryradio link, as explained above) and sets a flag in said secondaryvirtual power headroom report (e.g. the R- or V-flag in the last line ofthe PHR MAC CE as illustrated in FIG. 22). According to still anotheralternative, the UE prepares a virtual power headroom report for thesecondary radio link between the UE and the SeNB, and sets the virtualpower headroom value of the secondary virtual power headroom report to aparticular predetermined value (e.g. to a negative value); please notethat in this case, the secondary virtual power headroom value does notallow the MeNB to derive the information on the pathloss thereof. In anycase, the MeNB receives from the UE one of the above-noted indications(i.e. flags or pre-determined V-PH value) and can derive therefrom thatthe secondary radio link is inactive for the uplink.

In summary, the UE thus informs the SeNB/MeNB in one way or another,about the inactivity of the respective radio link to the other eNB (i.e.MeNB/SeNB). The SeNB/MeNB can then use the received indication to updatethe power distribution ratio such that all the output power for uplinktransmissions by the UE is assigned to the uplink transmissions over theradio link that remains “active”; i.e. the SeNB, when being informedabout the first radio link to the MeNB becoming inactive for the uplink,determines a new value for P_(EMAX,SeNB), with P_(EMAX,SeNB)=P_(CMAX)(or P_(CMAX) _(_) _(L)), and transmits same to the UE (e.g. in a MACCE), such that the UE applies this new value for the uplinktransmissions to the SeNB. Similarly, the MeNB, when being informedabout the secondary radio link to the SeNB becoming inactive for theuplink, determines a new value for P_(EMAX,MeNB), withP_(EMAX,MeNB)=P_(CMAX) (or P_(CMAX) _(_) _(L)), and transmits same tothe UE (e.g. in a MAC CE), such that the UE applies this new value forthe uplink transmissions to the MeNB.

However, since those inactivities of radio links are usually of atemporary nature, the power distribution ratio has to be eventuallyrestored to the previous ratio. To said end, the UE of course couldagain inform the MeNB/SeNB about the respective radio link to the othereNB (i.e. SeNB/MeNB) becoming active again, so as to trigger anotherreconfiguration of the power distribution ratio, in a similar manner asjust explained above.

According to another improvement of the present disclosure however, thissecond informing step of the UE, when a radio becomes active for theuplink again, is avoided by the use of a corresponding timer in theSeNB/MeNB. In more detail, the reconfiguration of the power distributionratio shall be only valid for a particular length of time, as configuredby a power control timer, implemented in the SeNB and MeNB to said end.After expiry of said power control timer, the power distribution beforethe re-configuration shall be applied again. In detail, a power controltimer is implemented in the SeNB and MeNB, which is respectivelytriggered, when the SeNB/MeNB receives the indication about the radiolink becoming inactive and the SeNB/MeNB calculates the new updatedvalue of the power output and sends it to the UE. Upon expiry of thepower control timer, the SeNB/MeNB returns the power distribution ratioto the ratio as applied before the re-configuration, and sends thethus-restored power parameter P_(EMAX,SeNB)/P_(EMAX,MeNB) to the UEagain.

The value of the power control timer can be either pre-configured; oreven more preferably may be instructed by the UE. Particularly, when theUE determines that a radio link becomes inactive for the uplink, the UEmay also determine the expected length of time the radio link isexpected to be inactive for the uplink. Then, the UE informs the SeNBrespectively MeNB about the expected length of inactivity time, wherethe SeNB and MeNB can use this information to configure its powercontrol timer. According to one advantageous implementation, the UE canencode the expected length of inactivity time into the virtual powerheadroom value of the secondary virtual power headroom report; e.g. thevirtual power headroom value not only encodes that the first/secondaryradio link becomes inactive (e.g. by using a negative virtual powerheadroom value), but would also encode the expected length of time ofthe inactivity (e.g. by use of different particular negative virtualpower headroom values).

Correspondingly, as explained above, when a radio link becomes inactivefor the uplink, the UE power distribution is re-configured such that theUE can use its full UE power resource for the other still-active radiolink.

In a similar manner, situations are dealt with where a radio linkbreaks, i.e. where the radio link is not usable any more for uplink (anddownlink) transmissions. The UE monitors the radio links for failure,and thus eventually will determine the radio link failure of one of thetwo radio links. Correspondingly, the UE shall inform the respectiveother eNB about the radio link failure; i.e. the UE shall inform theMeNB in case of a radio link failure of the secondary radio link to theSeNB; and the UE shall inform the SeNB in case of a radio link failureof the first radio link to the MeNB.

The UE may inform the SeNB/MeNB about the radio link failure of thefirst/secondary radio link e g in a similar manner as done for theabove-discussed cases of radio link inactivity for the uplink. In orderto avoid unnecessary repetition, please refer the above explanations onhow the different R- or V-flags of the various (virtual) power headroomreports or the (negative) virtual power headroom values could be reusedin said respect.

In summary, the UE informs the SeNB/MeNB in one way or another about theradio link failure of the respective radio link. The SeNB/MeNB can thenuse the received indication to update the power distribution ratio suchthat all the output power for uplink transmissions by the UE is assignedto uplink transmissions over the functioning radio link. In detail, theSeNB, when being informed about the radio link failure of the firstradio link, determines a new value for P_(EMAX,SeNB), withP_(EMAX,SeNB)=P_(CMAX) (or P_(CMAX) _(_) _(L)), and transmits same tothe UE (e.g. in a MAC CE), such that the UE applies this new value forthe uplink transmissions to the SeNB. Conversely, the MeNB, when beinginformed about the radio link failure of the secondary radio link,determines a new value for P_(EMAX,MeNB), with P_(EMAX,MeNB)=P_(CMAX)(or P_(CMAX) _(_) _(L)), and transmits same to the UE (e.g. in a MACCE), such that the UE applies this new value for the uplinktransmissions to the MeNB.

Furthermore, the SeNB/MeNB, when receiving the indication from the UE,about a radio link failure, can initiate appropriate procedures to solvethe radio link failure. For instance, when the MeNB learns about theradio link failure of the secondary radio link, it may change the radiobearers, which were going via the SeNB, to go via the MeNB, or it maydetermine another SeNB for the UE to connect to. Details of theseprocedures are already known in the prior art and thus known to theskilled person, and are thus omitted from this description.

On the other hand, when the SeNB learns about the radio link failure ofthe first radio link, it may perform a reconfiguration or handover suchthat the SeNB becomes the new MeNB. Details of this procedure arealready known in the prior art and thus known to the skilled person, andare thus omitted from this description. Depending on whether and how theradio link failure is solved, the power distribution ratio may beupdated again at a later point in time, new parameters P_(EMAX,SeNB),and/or P_(EMAX,MeNB), shall be determined and then provided again to theUE and/or MeNB/SeNB for appropriately configuring the power distributionof the UE.

Hardware and Software Implementation

Another embodiment of the present disclosure relates to theimplementation of the above described various embodiments using hardwareand software, or hardware only. In this connection the presentdisclosure provides a user equipment (mobile terminal) and a master andsecondary eNodeB (base station). The user equipment and base station areadapted to perform the methods described herein.

It is further recognized that the various embodiments of the presentdisclosure may be implemented or performed using computing devices(processors). A computing device or processor may for example be generalpurpose processors, digital signal processors (DSP), applicationspecific integrated circuits (ASIC), field programmable gate arrays(FPGA) or other programmable logic devices, etc. In addition, radiotransmitter and radio receiver and other necessary hardware may beprovided in the apparatuses (UE, MeNB, SeNB). The various embodiments ofthe present disclosure may also be performed or embodied by acombination of these devices.

Further, the various embodiments of the present disclosure may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments of the present disclosure may individually or in arbitrarycombination be subject matter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments without departing from the spirit orscope of the present disclosure as broadly described. The presentembodiments are, therefore, to be considered in all respects to beillustrative and not restrictive.

The invention claimed is:
 1. A mobile station for power headroomreporting in a mobile communication system comprising: circuitry, which,in operation, establishes a dual connectivity between the mobile stationand both a master base station via a first radio link and a secondarybase station via a secondary radio link, and generates a power headroomreport including a first power headroom report for the first radio link,using a first Media Access Control (MAC) entity which handles MACfunctionalities and protocol towards the master base station, calculatesa virtual power headroom report for an activated serving cell of thesecondary radio link based on a virtual uplink resource assignment forthe secondary radio link, when a virtual power headroom calculation isconfigured; and a transmitter, which, in operation, transmits the powerheadroom report including at least the first power headroom report fromthe mobile station to the master base station, wherein, when the virtualpower headroom calculation is configured, the power headroom reportalways additionally includes the virtual power headroom report for thesecondary radio link every time a power headroom reporting for the firstradio link is triggered.
 2. The mobile station according to claim 1,wherein the transmitter, in operation, transmits the power headroomreport including the first power headroom report and the virtual powerheadroom report in a single MAC Control Element.
 3. A method for powerheadroom reporting in a mobile communication system comprising:establishing a dual connectivity between a mobile station and both amaster base station via a first radio link and a secondary base stationvia a secondary radio link; generating, by the mobile station, a powerheadroom report including a first power headroom report for the firstradio link, using a first Media Access Control (MAC) entity whichhandles MAC functionalities and protocol towards the master basestation; calculating, by the mobile station, a virtual power headroomreport for an activated serving cell of the secondary radio link basedon a virtual uplink resource assignment for the secondary radio link,when a virtual power headroom calculation is configured; andtransmitting the power headroom report including at least the firstpower headroom report from the mobile station to the master basestation, wherein, when the virtual power headroom calculation isconfigured, the power secondary radio link every time a power headroomreporting for the first radio link is triggered.
 4. The method accordingto claim 3, wherein the power headroom report including the first powerheadroom report and the virtual power headroom report is transmitted ina single MAC Control Element.